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An updated review of the scientific literature on the origin of SARS-CoV-2


More than two and a half years have already passed since the first case of COVID-19 was officially reported (December 2019), as well as more than two years since the WHO declared the current pandemic (March 2020). During these months, the advances on the knowledge of the COVID-19 and SARS-CoV-2, the coronavirus responsible of the infection, have been very significant. However, there are still some weak points on that knowledge, being the origin of SARS-CoV-2 one of the most notorious. One year ago, I published a review focused on what we knew and what we need to know about the origin of that coronavirus, a key point for the prevention of potential future pandemics of a similar nature. The analysis of the available publications until July 2021 did not allow drawing definitive conclusions on the origin of SARS-CoV-2. Given the great importance of that issue, the present review was aimed at updating the scientific information on that origin. Unfortunately, there have not been significant advances on that topic, remaining basically the same two hypotheses on it. One of them is the zoonotic origin of SARS-CoV-2, while the second one is the possible leak of this coronavirus from a laboratory. Most recent papers do not include observational or experimental studies, being discussions and positions on these two main hypotheses. Based on the information here reviewed, there is not yet a definitive and well demonstrated conclusion on the origin of SARS-CoV-2.

Keywords: COVID-19; Hosts; Laboratory leak; SARS-CoV-2; Zoonotic origin.

Copyright © 2022. Published by Elsevier Inc.

Conflict of interest statement

Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Early Childhood Educators’ Well-Being: An Updated Review of the Literature

Early Childhood Education Journal volume  45 ,  pages 583–593 ( 2017 ) Cite this article

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Researchers are increasingly recognising the connections between early childhood educators’ well-being and their capacity for providing high quality education and care. The past five years have seen an intensification of research concerning early childhood educators’ well-being. However, fragmentation along conceptual, contextual and methodological lines makes it difficult to clearly identify the most effective focus for future research. The purpose of this article is to identify trends in, and implications of recent research concerned with educators’ well-being. Attention is given to ways recent studies address concerns raised in a review of earlier literature (Hall-Kenyon et al. in Early Child Educ J 42(3):153–162, 2014 , doi: 10.1007/s10643-013-0595-4 ), and what implications recent studies have for future research efforts concerned with educators’ well-being.

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As explained in the search procedures, crossover with the era of literature reviewed by Hall-Kenyon et al. ( 2014 ) was done deliberately. There is no duplication of studies reviewed between this current review and that of Hall-Kenyon et al.

It is possible that, despite searching numerous databases, there may be more studies concerned with educators’ well-being than have been covered in this review and in Hall-Kenyon et al.’s ( 2014 ). A search using the term ‘early childhood educators’ in journal articles published prior to 2012, or the inclusion of book chapters or dissertations could potentially expand the body of literature further.

Two articles by Rentzou reported on data from the same study, therefore I have counted one study only for this author.

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The author wishes to thank Professor Jennifer Sumsion for her generous advice and feedback on drafts of this article, as well as the helpful suggestions of the anonymous reviewers.

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Women and Birth

The nature of labour pain: an updated review of the literature.

The pain experience associated with labour is complex. Literature indicates psychosocial and environmental determinants of labour pain, and yet methods to support women usually target physiological attributes via pharmacological interventions.

To provide an update of our understanding of labour pain based on modern pain science. The review aims to help explain why women can experience labour pain so differently — why some cope well, whilst others experience great suffering. This understanding is pertinent to providing optimal support to women in labour.

A literature search was conducted in databases Medline, Cumulative Index to Nursing and Allied Health Literature and PsycINFO , using search terms labor/labour, childbirth , pain, experience and perception. Thirty-one papers were selected for inclusion.

Labour pain is a highly individual experience. It is a challenging, emotional and meaningful pain and is very different from other types of pain. Key determinants and influences of labour pain were identified and grouped into cognitive, social and environmental factors.

If a woman can sustain the belief that her pain is purposeful (i.e. her body working to birth her baby), if she interprets her pain as productive (i.e. taking her through a process to a desired goal) and the birthing environment is safe and supportive, it would be expected she would experience the pain as a non-threatening, transformative life event. Changing the conceptualisation of labour pain to a purposeful and productive pain may be one step to improving women’s experiences of it, and reducing their need for pain interventions.

The pain experience associated with labour is a complex phenomenon. It is often described as the most challenging and intense pain experience a woman may go through, and yet enormous variations in women’s perceptions of this pain exist. 1 Labour pain can be described as a paradoxical experience; one that is excruciating and yet desirable because of its positive outcome — the birth of a child. 2 Curiously, pain-free labours are not necessarily more satisfying to women 3 and many women desire to experience all the sensations of labour — including pain. 4

Labour pain has been defined as an “excellent model of acute pain”, 5 however unlike other acute pains that are usually associated with injury or pathology, labour pain is part of a normal physiological process. The pain associated with labour raises significant philosophical and theoretical questions due to its unique occurrence: Why is a normal physiological event, one that is essential to human existence, associated with such intense pain? From an evolutionary perspective labour may be painful in order to drive appropriate behaviour in the woman and others. That is, to capture the labouring woman’s attention and motivate her to seek help and safety. It is clear that there is still much to learn about the nature of labour pain.

In 2002 Nancy Lowe published ‘The Nature of Labor Pain’ 1 —a seminal literature review that was part of a broader project aiming to improve understandings of labour pain and its management (see Caton et al. 6 for more information). Lowe’s review summarised the literature regarding labour pain up until the year 2000, and interpreted this literature based on pain theories at the time. Over the past two decades shifts have occurred in both the characteristics of labouring women, the labour environment, and pain science. This present review aims to provide an update of our understanding of labour pain. It will capture and examine the literature since the start of the twenty-first century and aim to understand this literature in relation to the contemporary labouring woman and labour environment. Importantly, this literature will be evaluated in light of modern pain science.

This review aims to address the questions: What is the nature of labour pain? and What are the determinants and influences of labour pain? By the end of the review we hope to better understand why women can experience labour pain so differently. Why do some women cope well with labour pain, whilst others experience great suffering? These research questions have not been comprehensively addressed in the literature since Lowe’s 2002 review. And yet, this understanding is pertinent to providing optimal support to women going through such an experience.

Given the volume of literature on labour pain, this narrative review is intended to be illustrative as opposed to exhaustive. Studies will be selected for inclusion that contribute to better understanding the nature and influences of labour pain. In addition, we will raise a number of important related topics in order to put this review into context. These will include a description of ‘the contemporary labouring woman’, a summary of current pain theories, as well as important issues relating to assessing pain.

Over the last three decades, changes have occurred in the characteristics of the labouring woman, her labour environment and her pain management options. In 2015 the average age of a woman giving birth in Australia was 30.3 years, compared to 27.9 years in 1991.7, 8 A growing proportion of labouring women in both Australia and the United States (US) are aged 40 or older, are using assisted reproductive technology to assist with their conception, and have comorbidities such as obesity.8, 9, 10, 11

The management of women’s labours and births is also changing. The rate of spontaneous onset of labour in Australia has reduced to 56% and the rate of caesarean section has risen to 33%. 12 Similar trends are seen in the US with the caesarean rate at 32% of births. 11 Of mothers who experience labour, a large proportion receive analgesia: 85.7% for first-time mothers in Australia. 12 Women who do labour towards a vaginal birth are more likely to undergo continuous fetal monitoring 13 as well as induction or augmentation of their labours. 12

The contemporary labouring woman may now be able to access contemporary pain management options such as mobile epidurals, 14 intradermal water injections 15 and labour hypnosis. 16 She may also have more access to water during labour and birth 17 as well as alternatives to standard hospital care including continuity of care (group or case-load midwifery care) and team midwifery care. 18 In 2017 a Cochrane review reported the positive effects of continuous support during labour on women’s experience (including pain) and reduced use of analgesics. 19 At the same time, however, women’s labour and births are influenced by the medicalisation of labour, including hospital practices and the philosophies regarding management of labour and the birth environment. In an Australian study a critical analysis of hospital documents provided to women demonstrated how certain practices are framed as risky (use of water in labour) or safe (use of epidural analgesia during labour) depending on their acceptance by hospital culture, rather than their actual level of risk. 20 Low risk women giving birth in Australian private hospitals are more likely to receive obstetric interventions, such as an epidural or instrumental delivery, than low risk women in public hospitals.21, 22 Furthermore, a recent study in the US found that certain labour and delivery unit management cultures result in a higher rate of caesarean sections and complications, independent of women’s health. 23

The changing characteristics of the contemporary labouring women and her labour environment must be considered when attempting to understand her experience of labour pain and the determinants and influences of that experience.

The International Association for the Study of Pain (IASP) defines pain as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage”. 24 This widely recognised and accepted definition has been applied by the clinical and research community dealing with many different occurrences of pain, including the pain associated with childbirth. However, labour pain may be a pain experience that is not adequately captured by this conceptualisation. The IASP definition describes tissue damage (actual or potential) as the main attributor to the pain experience, and implies that the function of pain is to indicate bodily tissue damage (actual or potential). Neither of these points may apply to the pain associated with a normal labour where normal tissue changes are occurring to work towards the birth of a baby, and the function of the pain experience may be to encourage appropriate survival-related behaviours in the woman. 25 The unique context of the pain of labour, as well as its complexities, suggest that the current definition of pain may not always be appropriate.

Whilst modern understandings of pain (described below) further make sense of the complexities and individuality of the human pain experience it seems that labour pain has not yet made the conceptual shift toward these new understandings. The previously dominant biophysiologic model that defined pain as a sensory message of peripheral tissue damage persists in both research and management of labour pain. That is, in research the focus remains on measuring the sensory component of a woman’s pain, and labour pain management continues to primarily focus on obliterating the sensory input by pharmacological means. Our attempt to better understand labour pain must be based upon up-to-date theories of pain science.

The neuromatrix theory, introduced by Ronald Melzack in the early twenty-first century, explains that pain is produced by a matrix of neural structures in the brain in response to actual or perceived tissue threat. 26 Multiple inputs feed into the central processing areas of the brain to produce the experience of pain, including affective-emotional, cognitive-evaluative and sensory-discriminative. The important recognition of multiple inputs (and therefore multiple dimensions) helps us better understand the enormous variations in individuals’ pain experiences associated with seemingly similar physiological situations, such as labour. It gives emphasis to the non-biological contributions to a pain experience. Pain is not simply driven by the state of the tissues and nociceptive input into the central nervous system. Rather, it emerges from a complex integration of affective, cognitive and sensory constituents, and only emerges when the brain determines that there is a threat to the self and that the individual should know about it. What one person’s brain classifies as a ‘threat’ may be different from another’s. 27

Using the neuromatrix theory of pain as a theoretical basis, specific determinants and influences of the experience of pain continue to emerge from the literature. Most notably is the recognition of the complex role of cortical processes, such as beliefs, expectations and past experiences, in the perception of pain. 28 This complex processing is influenced by the meaning of the pain 29 and by the social context in which it occurs. 30 It is further shaped by the individual’s emotional state 31 and other features of their state of mind such as their tendency to catastrophise 32 or their ability to accept the experience (psychological flexibility). 33 This modern understanding of pain provides a useful framework for better understanding the complexities of labour pain. It also assists in understanding and supporting alternate pain paradigms for labour pain such as ‘working with pain’ 34 and for describing labour pain as ‘functional discomfort’. 35 Finally, a better understanding of labour pain is warranted considering the emerging body of work demonstrating the interactions between pain and women’s hormonal physiology during labour, in particular beta-endorphins and oxytocin. 36

Pain is an entirely subjective experience. In order for an observer to ‘know’ a person’s pain, the person must communicate it. They must transform that inner experience into words to describe it, and/or display ‘pain behaviours’ that can be interpreted by an observer. 37 The interpretation of pain behaviours is heavily dependent on the social and cultural learnings and understandings of both the person in pain and the observer. In addition, the words used to describe a person’s pain may be subject to individual interpretation.

Pain measurement tools, such as a Visual Analogue Scale (VAS), Numeric Rating Scale and the McGill Pain Scale are validated tools for both clinical and research use, and are frequently used in labour settings. These types of measures are a convenient method of objectifying what is a subjective phenomenon, particularly in large cohorts. They are relatively simple and quick measures to complete, and may allow a caregiver to ascertain the effectiveness of a pain intervention, or a labouring woman who is in need of assistance.

However these tools “don’t actually measure ‘pain’ but attempt to access, quantify (VAS) or qualify (burning, stinging) certain ‘dimensions’ of pain expression”. 37 Each measurement tool attempts to convert what is a multidimensional and meaningful felt experience into a number on a scale. For particularly complex pain experiences such as labour, significant limitations have been recognised in their use due to the dynamic and, for many women, extreme nature of this pain experience. Women themselves have identified the potential inaccuracies of such pain assessment tools due to emotional and attentional influences during labour, and express annoyance at the disruption caused by such assessments.38, 39 Numerous studies have identified a ceiling effect and issues with the interpretation of the ‘worse pain imaginable’ anchor of such scales.38, 40 A study by Roberts et al. 39 reported the development and implementation of an alternative to measuring pain in labour: a ‘Coping with Labor Algorithm’ which may provide a suitable alternative to caregivers to ascertain whether a women needs assistance.

Ultimately, it would seem that the closest we can get to understanding the complexities of a woman’s experience of labour pain is to listen to her pain story — to her self-selected words to describe the pain experience as it occurred within the social and cultural context of her life. It is for this reason that qualitative studies will be of major focus in this review in helping us answer our research questions.

Search strategy, selection and evaluation

Extensive searches were undertaken within the electronic databases Medline, Cumulative Index to Nursing and Allied Health Literature (CINAHL) and PsycINFO. Search terms used included labor/labour, childbirth and pain. The additional search terms of ‘experience’ and ‘perception’ were used (with the ‘or’ Boolean operand) in order to narrow the search to the concept of interest (women’s experience/perception of labour pain). An iterative process was used within each individual database using

Pain attributed to normal tissue-based changes of physiological labour

Numerous studies have previously demonstrated the association between the mean intensity of labour pain and labour progression, where higher ratings of pain correlate with increasing cervical dilation, as well as uterine contraction intensity, frequency and duration (see Lowe 1 ). It is important to note, however, that enormous variability in women’s pain ratings continue to be evident. For example, a study of 81 labouring women at 3   cm dilation reported a range of pain scores between 21 and 100

Our understanding of the complexities of labour pain is expanding. The recognition of these complexities is important as we continue to evolve our strategies of supporting the contemporary labouring women through such experiences. All individuals involved in the care of labouring women – from policy makers to those supporting her during her labour – should understand the determinants and influences of labour pain. Although incredibly intense and challenging, it is very different in nature to


The authors would like to thank Stav Hillel, La Trobe University Senior Learning Advisor, for his assistance with database searches. No financial assistance was provided for this project.

It’s beyond water: stories of women’s experience of using water for labour and birth

Women birth, how caregivers manage pain and distress in second-stage labor, j midwifery women’s health, requests for cesarean deliveries: the politics of labor pain and pain relief in shanghai, china, soc sci med, journey to confidence: women’s experiences of pain in labour and relational continuity of care, anxiety sensitivity as a predictor of labor pain, pain in childbirth and postpartum recovery: the role of catastrophizing, the range of coping strategies women use to manage pain and anxiety prior to and during first experience of labour, japanese women’s experiences of pharmacological pain relief in new zealand, women’s expectations and experiences with labour pain in medical and midwifery models of birth in the united states, women’s experiences of labour pain and the role of the mind: an exploratory study, swedish women’s experience of childbirth 2 years after birth, childbirth experience according to a group of brazilian primiparas, comparison of induction of labour and expectant management in postterm pregnancy: a matched cohort study, the coping with labor algorithm: an alternate pain assessment tool for the laboring woman, assessment of pain associated with childbirth: women’s perspectives, preferences and solutions, functional discomfort and a shift in midwifery paradigm, psychological flexibility in adults with chronic pain: a study of acceptance, mindfulness, and values-based action in primary care, documenting risk: a comparison of policy and information pamphlets for using epidural or water in labour, implementing caseload midwifery: exploring the views of maternity managers in australia—a national cross-sectional survey, the nature and management of labor pain: executive summary, am j obstet gynecol, labour pain as a model of acute pain, women’s experience of pain during childbirth, the nature of labor pain, epidural versus non-epidural or no analgesia in labour, cochrane database syst rev, pain is the club: identity and membership in the natural childbirth community, qual sociol rev, australia’s mothers and babies 2010, australia’s mothers and babies—2015 in brief, assisted reproductive technology in australia and new zealand 2014, prepregnancy body mass index by maternal characteristics and state: data from the birth certificate, 2014, births: final data for 2015, australia’s mothers and babies 2014—in brief, fetal monitoring: creating a culture of safety with informed choice, j perinat educ, high dose versus low dose opioid epidural regimens for pain relief in labour, intracutaneous or subcutaneous sterile water injection for relieving pain in labour, hypnosis for pain management during labour and childbirth, immersion in water in labour and birth, continuous support for women during childbirth, rates of obstetric intervention among low-risk women giving birth in private and public hospitals in nsw: a population-based descriptive study, psychological impact of hypnosis for pregnancy and childbirth: a systematic review.

The use of hypnosis as a complementary therapy in the perinatal field is expanding, however, there is little research for its impact on perinatal mental health. Here, we review studies that evaluate the effect of hypnosis on women's mental health and subjective experiences.

A systematic review was conducted according to the PRISMA protocol for articles with experimental designs of hypnosis that measured their impact on several psychological variables, such as the presence of symptoms of anxiety, depression or fear of childbirth. Studies were evaluated according to the Critical Appraisal Skills Program Checklists (CASP), and analyzed for their designs and intervention themes.

Seven studies were included and six themes emerged: preparation for birth and unexpected events; change in the perception and experience of pain; pregnant body as a natural process; connection with the baby during pregnancy; development of inner resources; and progressive relaxation and guided imagery. Although results were partly mitigated, most studies found positive effects of hypnosis in alleviating anxiety, depression, and fear towards birth, empowering women with a higher sense of confidence and improving the overall emotional experience. Two studies also indicate encouraging outcomes in postnatal wellbeing.

While it is still argued as to what extent hypnosis has positive effects on physical aspects of labor, the empowerment and the increase in confidence associated with hypnosis seem to bring a significant contribution to a more positive subjective experience of pregnancy and childbirth, and on women's overall wellbeing in the perinatal period.

Women's sense of control during labour and birth with epidural analgesia: A qualitative descriptive study

Sense of control during childbirth is a critical issue concerning the association between high-quality maternity care and infant health. This study explored the facilitators of or barriers to a sense of control and the need for interventions to raise women's experience in childbirth.

The data came from 17 participants. Data collection was conducted in the childbirth room and within three days following childbirth, respectively. For tackling the research problems, participant observation and interviewing were applied. Thematic analysis was applied to the data analyzed.

Two themes were identified: (1) facilitators of or barriers to practice a sense of control and (2) Care needed for a sense of control. The effectiveness of a sense of control is related to energy refill, mental loading subsided, control over decisions, non-pharmacological usage, and support from the meaningful person. Care needed includes showing empathy, providing information, using complementary pain-relief strategies, and adjusting care by parturient conditions.

This study highlights the influencing factors and interventions relating to women's sense of control during childbirth with epidural analgesia. The findings suggest that many approaches, such as white noise, benefit women's sense of control after an epidural. Using non-pharmacological methods, such as a birth ball, should be appropriately regulated by situations to enhance women's sense of control. Through the assessment, education, attention to maternal needs, and recognizing the barriers to a sense of control, women will benefit from the interventions designed to improve their sense of control during childbirth.

Predictors associated with low-risk women's pre-labour intention for intrapartum pain relief: a cross-sectional study

Pregnant women have preferences about how they intend to manage labour pain. Unmet intentions can result in negative emotions and/or birth experiences.

To examine the antenatal level of intention for intrapartum pain relief and the factors that might predict this intention.

A cross-sectional online survey-based study.

414 healthy pregnant women in the Netherlands, predominantly receiving antenatal care from the community-based midwife who were recruited via maternity healthcare professionals and social media platforms.

The attitude towards intrapartum pain relief was measured with the Labour Pain Relief Attitude Questionnaire for pregnant women. Personality traits with the HEXACO-60 questionnaire, general psychological health with the Mental Health Inventory-5 and labour and birth anxiety with the Tilburg Pregnancy Distress Scale. Multiple linear regression was performed with the intention for pain relief as the dependant variable.

The obstetrician as birth companion ( p <.001), the perception that because of the impact of pregnancy on the woman's body, using pain relief during labour is self-evident ( p <.001), feeling convinced that pain relief contributes to self-confidence during labour ( p =.023), and fear of the forthcoming birth ( p =.003) predicted women were more likely to use pain relief. The midwife as birth companion ( p =.047) and considering the partner in requesting pain relief ( p =.045) predicted women were less likely to use pain relief.

Understanding the reasons predicting women's intention of pain management during labour, provides insight in low-risk women's supportive needs prior to labour and are worth paying attention to during the antenatal period.

Women's perceptions of counselling on pain assessment and management during labour in Finland: A cross-sectional survey

The challenge is to identify pain assessment counselling that are effective and reliable to the woman during labour while also supporting appropriate management of labour pain.

This study aimed to describe women's perceptions of their counselling on pain assessment and pain management during labour.

A descriptive, cross-sectional study.

The sample consisted of women who had given birth (n=204) at a university hospital in Finland; 250 parturients were recruited by convenience sampling.

Data were collected using a questionnaire (P-PAPM) between November 2018 and February 2019. The statistical significance of observed differences was analysed using the Chi-squared test and Fischer's exact test.

Eighty percent of women reported that they had received counselling on pharmacological treatments from midwives, but only 33 % received counselling on pain assessment. The non-pharmacological methods for alleviating labour pain most commonly taught by midwives were proper breathing techniques, cold/heat treatments, and trying different positions and movements. Women were less commonly counselled to try listening to music, thinking about pleasant and positive things, or concentrating their thoughts on something other than pain. The two most commonly used counselling methods were demonstrations and written material and least used Internet-based resources. The personal issue that midwives discussed most frequently during counselling was the women's individual hopes concerning pain management (91%), while the issue discussed least often was previous experiences of pain (58%). The participants’ experiences of fear, age, and education were significantly associated with aspects of counselling on pain assessment and management.

Women's counselling on pain assessment and management during labour varied widely. Therefore, to improve its quality, counselling should be routinely integrated into daily midwifery work. In particular, the counselling given on non-pharmacological pain relief methods during labour was inadequate. More varied counselling methods should be used in the future. Finally, the results indicate that midwives’ knowledge of counselling should be increased and they should be encouraged to routinely offer counselling on pain assessment and management for parturing women.

Effects of acupressure and shower applied in the delivery on the intensity of labor pain and postpartum comfort

Labour pain is a constantly increasing pain. This study thus aims to determine the effects of acupressure and shower on labour pain and postpartum comfort.

In this randomized controlled trial (RCT), the control group consisted of 40 pregnant women, while the experimental groups consisted of 80 pregnant women in total. The experimental groups received routine labour care and either acupressure or showers upon reaching three cervical dilations (4–5, 6–7 and 8–10 cm). The control group only received routine labour care. A maternal information form (MIF), the Visual Analog Scale (VAS) and the Postpartum Comfort Questionnaire (PPCQ) were used to collect data.

Pain was significantly reduced in both of the experimental groups, in contrast to the control group, in all periods of the study (p < 0.001). Postpartum comfort also significantly increased in the experimental groups compared to the control group (p < 0.05).

Acupressure and showering are effective in reducing labour pain and increasing postpartum comfort. Midwives and nurses can therefore apply them as inexpensive and easy to administer methods for labour pain relief.

Epidural use among women with spontaneous onset of labour – an observational study using data from a cluster-randomised controlled trial

To investigate whether the proportion of pregnant women who use epidural analgesia during birth differed between women registered at a maternity clinic randomised to Mindfetalness or to routine care.

An observational study including women born in Sweden with singleton pregnancies, with spontaneous onset of labour from 32 weeks’ gestation. Data used from a cluster-randomised controlled trial applying the intention-to-treat principle in 67 maternity clinics where women were randomised to Mindfetalness or to routine care. ClinicalTrials.gov (NCT02865759).

Midwives were instructed to distribute a leaflet about Mindfetalness to pregnant women at 25 weeks’ gestation. Mindfetalness is a self-assessment method for the woman to use to become familiar with the unborn baby's fetal movement pattern. When practising the method in third trimester, the women are instructed to daily lie down on their side, when the baby is awake, and focus on the movements’ intensity, character and frequency (but not to count each movement).

Of the 18 501 women with spontaneous onset of labour, 47 percent used epidural during birth. Epidural was used to a lower extent among women registered at a maternity clinic randomised to Mindfetalness than women in the routine-care group (46.2% versus 47.8%, RR 0.97, CI 0.94–1.00, p = 0.04). Epidural was more common among primiparous women, women younger than 35 years, those with educational levels below university, with BMI ≥25 and with a history of receiving psychiatric care or psychological treatment for mental illness.

Pregnant women who were informed about a self-assessment method, with the aim of becoming familiar with the unborn baby's fetal movement pattern, used epidural to a lower extent than women who were not informed about the method. Future studies are needed to investigate and understand the association between Mindfetalness and the reduced usage of epidural during birth.

Women with fear of childbirth might benefit from having a known midwife during labour

Having a known midwife at birth is valued by women across the world, however it is unusual for women with fear of childbirth to have access to this model of care. The aim of this study was to describe the prevalence and factors related to having access to a known midwife for women referred to counseling due to childbirth fear. We also wanted to explore if women’s levels of childbirth fear changed over time.

A pilot study of 70 women referred to counseling due to fear of birth in 3 Swedish hospitals, and where the counseling midwife, when possible, also assisted during labour and birth.

34% of the women actually had a known midwife during labour and birth. Women who had a known midwife had significantly more counseling visits, they viewed the continuity of care as more important, were more satisfied with the counseling and 29% reported that their fear disappeared. Fear of birth decreased significantly over time for all women irrespective of whether they were cared for in labour by a known midwife or not.

Although the women in the present study had limited access to a known midwife, the results indicate that having a known midwife whom the women met on several occasions made them more satisfied with the counseling and had a positive effect on their fear. Building a trustful midwife–woman relationship rather than counseling per se could be the key issue when it comes to fear of birth.

Awareness of Listeriosis and Methylmercury toxicity public health recommendations and diet during pregnancy

Awareness of Listeriosis and Methylmercury toxicity recommendations are associated with decreased intake of high-risk foods. Whether awareness of the recommendations affect dietary quality of pregnant women in Australian is unknown.

To evaluate awareness of Listeriosis and Methylmercury toxicity recommendations during pregnancy and its impact on dietary quality.

Pregnant women (n   =   81) were recruited from antenatal clinics. Awareness of Listeriosis and Methylmercury toxicity recommendations and high-risk foods consumption were assessed via questionnaire at 10–23 weeks gestation. Diet quality was measured using the 2005 Healthy Eating Index using a validated food frequency questionnaire at 10–23 and 34–36 weeks gestation.

A higher proportion of women were aware of Methylmercury toxicity compared with Listeriosis recommendations (75.3 vs. 59.2%, p   <   0.001). The proportion of women who decreased or avoided consumption of certain high-risk Listeriosis foods were higher in those who were aware compared with those who were unaware of Listeriosis recommendations [raw fish (96.0 vs 69.2%, p   =   0.046), soft-serve ice cream (93.9 vs 58.3%, p   =   0.004) and alfalfa/bean sprouts (68.7 vs 28.5%, p   =   0.006)]. A large proportion of women (96.8%) met recommendations for limiting consumption of high Methylmercury fish. There was no difference in the change in dietary quality over pregnancy regardless of women’s awareness of the recommendations.

Awareness of Listeriosis and Methylmercury toxicity recommendations has little impact on dietary quality of pregnant women in this small study. Further research in a large representative population of pregnant women is needed to confirm our findings and to optimise dietary quality during pregnancy.

Joys and challenges of relationships in Scotland and New Zealand rural midwifery: A multicentre study

Globally there are challenges meeting the recruitment and retention needs for rural midwifery. Rural practice is not usually recognised as important and feelings of marginalisation amongst this workforce are apparent. Relationships are interwoven throughout midwifery and are particularly evident in rural settings. However, how these relationships are developed and sustained in rural areas is unclear.

To study the significance of relationships in rural midwifery and provide insights to inform midwifery education.

Multi-centre study using online surveys and discussion groups across New Zealand and Scotland. Descriptive and template analysis were used to organise, examine and analyse the qualitative data.

Rural midwives highlighted how relationships with health organisations, each other and women and their families were both a joy and a challenge. Social capital was a principal theme. Subthemes were (a) working relationships, (b) respectful communication, (c) partnerships, (d) interface tensions, (e) gift of time facilitates relationships.

To meet the challenges of rural practice the importance of relationship needs acknowledging. Relationships are created, built and sustained at a distance with others who have little appreciation of the rural context. Social capital for rural midwives is thus characterised by social trust, community solidarity, shared values and working together for mutual benefit. Rural communities generally exhibit high levels of social capital and this is key to sustainable rural midwifery practice.

Midwives, educationalists and researchers need to address the skills required for building social capital in rural midwifery practice. These skills are important in midwifery pre- and post-registration curricula.

Women׳s experiences of coping with pain during childbirth: A critical review of qualitative research

to identify and analyse qualitative literature exploring women׳s experiences of coping with pain during childbirth.

critical review of qualitative research.

ten studies were included, conducted in Australia, England, Finland, Iceland, Indonesia, Iran and Sweden. Eight of the studies employed a phenomenological perspective with the remaining two without a specific qualitative methodological perspective. Thematic analysis was used as the approach for synthesising the data in this review. Two main themes emerged as the most significant influences upon a woman׳s ability to cope with pain: (i) the importance of individualised, continuous support and (ii) an acceptance of pain during childbirth. This review found that women felt vulnerable during childbirth and valued the relationships they had with health professionals. Many of the women perceived childbirth pain as challenging, however, they described the inherent paradox for the need for pain to birth their child. This allowed them to embrace the pain subsequently enhancing their coping ability.

women׳s experience of coping with pain during childbirth is complex and multifaceted. Many women felt the need for effective support throughout childbirth and described the potential implications where this support failed to be provided. Feeling safe through the concept of continuous support was a key element of care to enhance the coping ability and avoid feelings of loneliness and fear. A positive outlook and acceptance of pain was acknowledged by many of the women, demonstrating the beneficial implications for coping ability. These findings were consistent despite the socio-economic, cultural and contextual differences observed within the studies suggesting that experiences of coping with pain during childbirth are universal.

the findings suggest there is a dissonance between what women want in order to enhance their ability to cope with pain and the reality of clinical practice. This review found women would like health professionals to maintain a continuous presence throughout childbirth and support a social model of care that promotes continuity of care and an increasing acceptance of pain as part of normal childbirth. It is suggested future research regarding the role of antenatal provision for instilling such a viewpoint in preparation of birth be undertaken to inform policy makers. The need for a shift in societal norms is also suggested to disseminate expectations and positive or negative views of what the role of pain during childbirth should be to empower women to cope with childbirth and embrace this transition to motherhood as part of a normal process.

Pain management during labor and vaginal birth

Neuraxial analgesia provides excellent pain relief in labor. Optimizing initiation and maintenance of neuraxial labor analgesia requires different strategies. Combined spinal-epidurals or dural puncture epidurals may offer advantages over traditional epidurals. Ultrasound is useful in certain patients. Maintenance of analgesia is best achieved with a background regimen (either programmed intermittent boluses or a continuous epidural infusion) supplemented with patient-controlled epidural analgesia and using dilute local anesthetics combined with opioids such as fentanyl. Nitrous oxide and systemic opioids are also used for pain relief. Nitrous oxide may improve satisfaction despite variable effects on pain. Systemic opioids can be administered by healthcare providers or using patient-controlled analgesia. Appropriate choice of drug should take into account the stage and progression of labor, local safety protocols, and maternal and fetal/neonatal side effects. Pain in labor is complex, and women should fully participate in the decision-making process before any one modality is selected.

Experiences of early labour management from perspectives of women, labour companions and health professionals: A systematic review of qualitative evidence

to examine evidence of women's, labour companions’ and health professionals’ experiences of management of early labour to consider how this could be enhanced to better reflect women's needs.

a systematic review of qualitative evidence.

women in early labour with term, low risk singleton pregnancies, not booked for a planned caesarean birth or post-dates induction of labour, their labour companions, and health professionals responsible for early labour care (e.g. midwives, nurse-midwives, obstetricians, family doctors). Studies from high and middle income country settings were considered.

21 publications were included from the UK, Ireland, Scandinavia, USA, Italy and New Zealand. Key findings included the impact of communication with health professionals (most usually midwives) on women's decision making; women wanting to be listened to by sympathetic midwives who could reassure that symptoms and signs of early labour were ‘normal’ and offer clear advice on what to do. Antenatal preparation which included realistic information on what to expect when labour commenced was important and appreciated by women and labour companions. Views of the optimal place for women to remain and allow early labour to progress differed and the perceived benefit of support and help offered by labour companions varied. Some were supportive and helped women to relax, while others were anxious and encouraged women to seek early admission to the planned place of birth. Web-based sources of information are increasingly used by women, with mixed views of the value of information accessed.

women, labour companions and health professionals find early labour difficult to manage well, with women unsure of how decisions about admission to their planned place of birth are taken. It is unclear why women are effectively left to manage this aspect of their labour with minimal guidance or support. Tailoring management to meet individual needs, with provision of effective communication could reassure women and facilitate timely admission from perspectives of women, their companions, midwives and other health professionals. Information on labour onset and progress, and approaches to pain management, should be shared with women's labour companions to enable them to feel more confident to better support women. Further research is needed of the impact of different models of care and increasing use of web-based information on women's approaches to self-management when labour commences.

PROSPERO 2014 CRD 42014009745

Gulf War and Health: Updated Literature Review of Sarin


Gulf War and Health

Updated literature review of sarin.

The Gulf War in 1990-1991 was considered a brief and successful military operation, with few injuries or deaths of US troops. The war began in August 1990, and the last US ground troops returned home by June 1991. Although most Gulf War veterans resumed their normal activities, many soon began reporting a variety of nonexplained health problems that they attributed to their participation in the Gulf War, including chronic fatigue, muscle and joint pain, loss of concentration, forgetfulness, headache, and rash. Because of concerns about the veterans' health problems, the Department of Veterans Affairs (VA) requested that the Institute of Medicine (IOM) review the scientific and medical literature on the long-term adverse health effects of agents to which the Gulf War veterans may have been exposed. This report is a broad overview of the toxicology of sarin and cyclosarin. It assesses the biologic plausibility with respect to the compounds in question and health effects.

Suggested Citation

Institute of Medicine. 2004. Gulf War and Health: Updated Literature Review of Sarin . Washington, DC: The National Academies Press. https://doi.org/10.17226/11064. Import this citation to: Bibtex EndNote Reference Manager

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Literature Reviews

What this handout is about.

This handout will explain what literature reviews are and offer insights into the form and construction of literature reviews in the humanities, social sciences, and sciences.


OK. You’ve got to write a literature review. You dust off a novel and a book of poetry, settle down in your chair, and get ready to issue a “thumbs up” or “thumbs down” as you leaf through the pages. “Literature review” done. Right?

Wrong! The “literature” of a literature review refers to any collection of materials on a topic, not necessarily the great literary texts of the world. “Literature” could be anything from a set of government pamphlets on British colonial methods in Africa to scholarly articles on the treatment of a torn ACL. And a review does not necessarily mean that your reader wants you to give your personal opinion on whether or not you liked these sources.

What is a literature review, then?

A literature review discusses published information in a particular subject area, and sometimes information in a particular subject area within a certain time period.

A literature review can be just a simple summary of the sources, but it usually has an organizational pattern and combines both summary and synthesis. A summary is a recap of the important information of the source, but a synthesis is a re-organization, or a reshuffling, of that information. It might give a new interpretation of old material or combine new with old interpretations. Or it might trace the intellectual progression of the field, including major debates. And depending on the situation, the literature review may evaluate the sources and advise the reader on the most pertinent or relevant.

But how is a literature review different from an academic research paper?

The main focus of an academic research paper is to develop a new argument, and a research paper is likely to contain a literature review as one of its parts. In a research paper, you use the literature as a foundation and as support for a new insight that you contribute. The focus of a literature review, however, is to summarize and synthesize the arguments and ideas of others without adding new contributions.

Why do we write literature reviews?

Literature reviews provide you with a handy guide to a particular topic. If you have limited time to conduct research, literature reviews can give you an overview or act as a stepping stone. For professionals, they are useful reports that keep them up to date with what is current in the field. For scholars, the depth and breadth of the literature review emphasizes the credibility of the writer in his or her field. Literature reviews also provide a solid background for a research paper’s investigation. Comprehensive knowledge of the literature of the field is essential to most research papers.

Who writes these things, anyway?

Literature reviews are written occasionally in the humanities, but mostly in the sciences and social sciences; in experiment and lab reports, they constitute a section of the paper. Sometimes a literature review is written as a paper in itself.

Let’s get to it! What should I do before writing the literature review?

If your assignment is not very specific, seek clarification from your instructor:

Find models

Look for other literature reviews in your area of interest or in the discipline and read them to get a sense of the types of themes you might want to look for in your own research or ways to organize your final review. You can simply put the word “review” in your search engine along with your other topic terms to find articles of this type on the Internet or in an electronic database. The bibliography or reference section of sources you’ve already read are also excellent entry points into your own research.

Narrow your topic

There are hundreds or even thousands of articles and books on most areas of study. The narrower your topic, the easier it will be to limit the number of sources you need to read in order to get a good survey of the material. Your instructor will probably not expect you to read everything that’s out there on the topic, but you’ll make your job easier if you first limit your scope.

Keep in mind that UNC Libraries have research guides and to databases relevant to many fields of study. You can reach out to the subject librarian for a consultation: https://library.unc.edu/support/consultations/ .

And don’t forget to tap into your professor’s (or other professors’) knowledge in the field. Ask your professor questions such as: “If you had to read only one book from the 90’s on topic X, what would it be?” Questions such as this help you to find and determine quickly the most seminal pieces in the field.

Consider whether your sources are current

Some disciplines require that you use information that is as current as possible. In the sciences, for instance, treatments for medical problems are constantly changing according to the latest studies. Information even two years old could be obsolete. However, if you are writing a review in the humanities, history, or social sciences, a survey of the history of the literature may be what is needed, because what is important is how perspectives have changed through the years or within a certain time period. Try sorting through some other current bibliographies or literature reviews in the field to get a sense of what your discipline expects. You can also use this method to consider what is currently of interest to scholars in this field and what is not.

Strategies for writing the literature review

Find a focus.

A literature review, like a term paper, is usually organized around ideas, not the sources themselves as an annotated bibliography would be organized. This means that you will not just simply list your sources and go into detail about each one of them, one at a time. No. As you read widely but selectively in your topic area, consider instead what themes or issues connect your sources together. Do they present one or different solutions? Is there an aspect of the field that is missing? How well do they present the material and do they portray it according to an appropriate theory? Do they reveal a trend in the field? A raging debate? Pick one of these themes to focus the organization of your review.

Convey it to your reader

A literature review may not have a traditional thesis statement (one that makes an argument), but you do need to tell readers what to expect. Try writing a simple statement that lets the reader know what is your main organizing principle. Here are a couple of examples:

The current trend in treatment for congestive heart failure combines surgery and medicine. More and more cultural studies scholars are accepting popular media as a subject worthy of academic consideration.

Consider organization

You’ve got a focus, and you’ve stated it clearly and directly. Now what is the most effective way of presenting the information? What are the most important topics, subtopics, etc., that your review needs to include? And in what order should you present them? Develop an organization for your review at both a global and local level:

First, cover the basic categories

Just like most academic papers, literature reviews also must contain at least three basic elements: an introduction or background information section; the body of the review containing the discussion of sources; and, finally, a conclusion and/or recommendations section to end the paper. The following provides a brief description of the content of each:

Organizing the body

Once you have the basic categories in place, then you must consider how you will present the sources themselves within the body of your paper. Create an organizational method to focus this section even further.

To help you come up with an overall organizational framework for your review, consider the following scenario:

You’ve decided to focus your literature review on materials dealing with sperm whales. This is because you’ve just finished reading Moby Dick, and you wonder if that whale’s portrayal is really real. You start with some articles about the physiology of sperm whales in biology journals written in the 1980’s. But these articles refer to some British biological studies performed on whales in the early 18th century. So you check those out. Then you look up a book written in 1968 with information on how sperm whales have been portrayed in other forms of art, such as in Alaskan poetry, in French painting, or on whale bone, as the whale hunters in the late 19th century used to do. This makes you wonder about American whaling methods during the time portrayed in Moby Dick, so you find some academic articles published in the last five years on how accurately Herman Melville portrayed the whaling scene in his novel.

Now consider some typical ways of organizing the sources into a review:

Sometimes, though, you might need to add additional sections that are necessary for your study, but do not fit in the organizational strategy of the body. What other sections you include in the body is up to you. Put in only what is necessary. Here are a few other sections you might want to consider:

Questions for Further Research: What questions about the field has the review sparked? How will you further your research as a result of the review?

Begin composing

Once you’ve settled on a general pattern of organization, you’re ready to write each section. There are a few guidelines you should follow during the writing stage as well. Here is a sample paragraph from a literature review about sexism and language to illuminate the following discussion:

However, other studies have shown that even gender-neutral antecedents are more likely to produce masculine images than feminine ones (Gastil, 1990). Hamilton (1988) asked students to complete sentences that required them to fill in pronouns that agreed with gender-neutral antecedents such as “writer,” “pedestrian,” and “persons.” The students were asked to describe any image they had when writing the sentence. Hamilton found that people imagined 3.3 men to each woman in the masculine “generic” condition and 1.5 men per woman in the unbiased condition. Thus, while ambient sexism accounted for some of the masculine bias, sexist language amplified the effect. (Source: Erika Falk and Jordan Mills, “Why Sexist Language Affects Persuasion: The Role of Homophily, Intended Audience, and Offense,” Women and Language19:2).

Use evidence

In the example above, the writers refer to several other sources when making their point. A literature review in this sense is just like any other academic research paper. Your interpretation of the available sources must be backed up with evidence to show that what you are saying is valid.

Be selective

Select only the most important points in each source to highlight in the review. The type of information you choose to mention should relate directly to the review’s focus, whether it is thematic, methodological, or chronological.

Use quotes sparingly

Falk and Mills do not use any direct quotes. That is because the survey nature of the literature review does not allow for in-depth discussion or detailed quotes from the text. Some short quotes here and there are okay, though, if you want to emphasize a point, or if what the author said just cannot be rewritten in your own words. Notice that Falk and Mills do quote certain terms that were coined by the author, not common knowledge, or taken directly from the study. But if you find yourself wanting to put in more quotes, check with your instructor.

Summarize and synthesize

Remember to summarize and synthesize your sources within each paragraph as well as throughout the review. The authors here recapitulate important features of Hamilton’s study, but then synthesize it by rephrasing the study’s significance and relating it to their own work.

Keep your own voice

While the literature review presents others’ ideas, your voice (the writer’s) should remain front and center. Notice that Falk and Mills weave references to other sources into their own text, but they still maintain their own voice by starting and ending the paragraph with their own ideas and their own words. The sources support what Falk and Mills are saying.

Use caution when paraphrasing

When paraphrasing a source that is not your own, be sure to represent the author’s information or opinions accurately and in your own words. In the preceding example, Falk and Mills either directly refer in the text to the author of their source, such as Hamilton, or they provide ample notation in the text when the ideas they are mentioning are not their own, for example, Gastil’s. For more information, please see our handout on plagiarism .

Revise, revise, revise

Draft in hand? Now you’re ready to revise. Spending a lot of time revising is a wise idea, because your main objective is to present the material, not the argument. So check over your review again to make sure it follows the assignment and/or your outline. Then, just as you would for most other academic forms of writing, rewrite or rework the language of your review so that you’ve presented your information in the most concise manner possible. Be sure to use terminology familiar to your audience; get rid of unnecessary jargon or slang. Finally, double check that you’ve documented your sources and formatted the review appropriately for your discipline. For tips on the revising and editing process, see our handout on revising drafts .

Works consulted

We consulted these works while writing this handout. This is not a comprehensive list of resources on the handout’s topic, and we encourage you to do your own research to find additional publications. Please do not use this list as a model for the format of your own reference list, as it may not match the citation style you are using. For guidance on formatting citations, please see the UNC Libraries citation tutorial . We revise these tips periodically and welcome feedback.

Anson, Chris M., and Robert A. Schwegler. 2010. The Longman Handbook for Writers and Readers , 6th ed. New York: Longman.

Jones, Robert, Patrick Bizzaro, and Cynthia Selfe. 1997. The Harcourt Brace Guide to Writing in the Disciplines . New York: Harcourt Brace.

Lamb, Sandra E. 1998. How to Write It: A Complete Guide to Everything You’ll Ever Write . Berkeley: Ten Speed Press.

Rosen, Leonard J., and Laurence Behrens. 2003. The Allyn & Bacon Handbook , 5th ed. New York: Longman.

Troyka, Lynn Quittman, and Doug Hesse. 2016. Simon and Schuster Handbook for Writers , 11th ed. London: Pearson.

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When and how to update systematic reviews: consensus and checklist

Peer review

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Updating of systematic reviews is generally more efficient than starting all over again when new evidence emerges, but to date there has been no clear guidance on how to do this. This guidance helps authors of systematic reviews, commissioners, and editors decide when to update a systematic review, and then how to go about updating the review.

Systematic reviews synthesise relevant research around a particular question. Preparing a systematic review is time and resource consuming, and provides a snapshot of knowledge at the time of incorporation of data from studies identified during the latest search. Newly identified studies can change the conclusion of a review. If they have not been included, this threatens the validity of the review, and, at worst, means the review could mislead. For patients and other healthcare consumers, this means that care and policy development might not be fully informed by the latest research; furthermore, researchers could be misled and carry out research in areas where no further research is actually needed. 1 Thus, there are clear benefits to updating reviews, rather than duplicating the entire process as new evidence emerges or new methods develop. Indeed, there is probably added value to updating a review, because this will include taking into account comments and criticisms, and adoption of new methods in an iterative process. 2 3 4 5 6

Cochrane has over 20 years of experience with preparing and updating systematic reviews, with the publication of over 6000 systematic reviews. However, Cochrane’s principle of keeping all reviews up to date has not been possible, and the organisation has had to adapt: from updating when new evidence becomes available, 7 to updating every two years, 8 to updating based on need and priority. 9 This experience has shown that it is not possible, sensible, or feasible to continually update all reviews all the time. Other groups, including guideline developers and journal editors, adopt updating principles (as applied, for example, by the Systematic Reviews journal; https://systematicreviewsjournal.biomedcentral.com/ ).

The panel for updating guidance for systematic reviews (PUGs) group met to draw together experiences and identify a common approach. The PUGs guidance can help individuals or academic teams working outside of a commissioning agency or Cochrane, who are considering writing a systematic review for a journal or to prepare for a research project. The guidance could also help these groups decide whether their effort is worthwhile.

Summary points

Updating systematic reviews is, in general, more efficient than starting afresh when new evidence emerges. The panel for updating guidance for systematic reviews (PUGs; comprising review authors, editors, statisticians, information specialists, related methodologists, and guideline developers) met to develop guidance for people considering updating systematic reviews. The panel proposed the following:

Decisions about whether and when to update a systematic review are judgments made for individual reviews at a particular time. These decisions can be made by agencies responsible for systematic review portfolios, journal editors with systematic review update services, or author teams considering embarking on an update of a review.

The decision needs to take into account whether the review addresses a current question, uses valid methods, and is well conducted; and whether there are new relevant methods, new studies, or new information on existing included studies. Given this information, the agency, editors, or authors need to judge whether the update will influence the review findings or credibility sufficiently to justify the effort in updating it.

Review authors and commissioners can use a decision framework and checklist to navigate and report these decisions with “update status” and rationale for this status. The panel noted that the incorporation of new synthesis methods (such as Grading of Recommendations Assessment, Development and Evaluation (GRADE)) is also often likely to improve the quality of the analysis and the clarity of the findings.

Given a decision to update, the process needs to start with an appraisal and revision of the background, question, inclusion criteria, and methods of the existing review.

Search strategies should be refined, taking into account changes in the question or inclusion criteria. An analysis of yield from the previous edition, in relation to databases searched, terms, and languages can make searches more specific and efficient.

In many instances, an update represents a new edition of the review, and authorship of the new version needs to follow criteria of the International Committee of Medical Journal Editors (ICMJE). New approaches to publishing licences could help new authors build on and re-use the previous edition while giving appropriate credit to the previous authors.

The panel also reflected on this guidance in the context of emerging technological advances in software, information retrieval, and electronic linkage and mining. With good synthesis and technology partnerships, these advances could revolutionise the efficiency of updating in the coming years.

Panel selection and procedures

An international panel of authors, editors, clinicians, statisticians, information specialists, other methodologists, and guideline developers was invited to a two day workshop at McMaster University, Hamilton, Canada, on 26-27 June 2014, organised by Cochrane. The organising committee selected the panel (web appendix 1). The organising committee invited participants, put forward the agenda, collected background materials and literature, and drafted the structure of the report.

The purpose of the workshop was to develop a common approach to updating systematic reviews, drawing on existing strategies, research, and experience of people working in this area. The selection of participants aimed on broad representation of different groups involved in producing systematic reviews (including authors, editors, statisticians, information specialists, and other methodologists), and those using the reviews (guideline developers and clinicians). Participants within these groups were selected on their expertise and experience in updating, in previous work developing methods to assess reviews, and because some were recognised for developing approaches within organisations to manage updating strategically. We sought to identify general approaches in this area, and not be specific to Cochrane; although inevitably most of the panel were somehow engaged in Cochrane.

The workshop structure followed a series of short presentations addressing key questions on whether, when, and how to update systematic reviews. The proceedings included the management of authorship and editorial decisions, and innovative and technological approaches. A series of small group discussions followed each question, deliberating content, and forming recommendations, as well as recognising uncertainties. Large group, round table discussions deliberated further these small group developments. Recommendations were presented to an invited forum of individuals with varying levels of expertise in systematic reviews from McMaster University (of over 40 people), widely known for its contributions to the field of research evidence synthesis. Their comments helped inform the emerging guidance.

The organising committee became the writing committee after the meeting. They developed the guidance arising from the meeting, developed the checklist and diagrams, added examples, and finalised the manuscript. The guidance was circulated to the larger group three times, with the PUGs panel providing extensive feedback. This feedback was all considered and carefully addressed by the writing committee. The writing committee provided the panel with the option of expressing any additional comments from the general or specific guidance in the report, and the option for registering their own view that might differ to the guidance formed and their view would be recorded in an annex. In the event, consensus was reached, and the annex was not required.

Definition of update

The PUGs panel defined an update of a systematic review as a new edition of a published systematic review with changes that can include new data, new methods, or new analyses to the previous edition. This expands on a previous definition of a systematic review update. 10 An update asks a similar question with regard to the participants, intervention, comparisons, and outcomes (PICO) and has similar objectives; thus it has similar inclusion criteria. These inclusion criteria can be modified in the light of developments within the topic area with new interventions, new standards, and new approaches. Updates will include a new search for potentially relevant studies and incorporate any eligible studies or data; and adjust the findings and conclusions as appropriate. Box 1 provides some examples.

Box 1: Examples of what factors might change in an updated systematic review

A systematic review of steroid treatment in tuberculosis meningitis used GRADE methods and split the composite outcome in the original review of death plus disability into its two components. This improved the clarity of the reviews findings in relation to the effects and the importance of the effects of steroids on death and on disability. 11

A systematic review of dihydroartemisinin-piperaquine (DHAP) for treating malaria was updated with much more detailed analysis of the adverse effect data from the existing trials as a result of questions raised by the European Medicines Agency. Because the original review included other comparisons, the update required extracting only the DHAP comparisons from the original review, and a modification of the title and the PICO. 12

A systematic review of atorvastatin was updated with simple uncontrolled studies. 13 This update allowed comparisons with trials and strengthened the review findings. 14

Which systematic reviews should be updated and when?

Any group maintaining a portfolio of systematic reviews as part of their normative work, such as guidelines panels or Cochrane review groups, will need to prioritise which reviews to update. Box 2 presents the approaches used by the Agency for HealthCare Research and Quality (AHRQ) and Cochrane to prioritise which systematic reviews to update and when. Clearly, the responsibility for deciding which systematic reviews should be updated and when they will be updated will vary: it may be centrally organised and resourced, as with the AHRQ scientific resource centre (box 2). In Cochrane, the decision making process is decentralised to the Cochrane Review Group editorial team, with different approaches applied, often informally.

Box 2: Examples of how different organisations decide on updating systematic reviews

Agency for healthcare research and quality (us).

The AHRQ uses a needs based approach; updating systematic reviews depends on an assessment of several criteria:

Stakeholder impact

Interest from stakeholder partners (such as consumers, funders, guideline developers, clinical societies, James Lind Alliance)

Use and uptake (for example, frequency of citations and downloads)

Citation in scientific literature including clinical practice guidelines

Currency and need for update

New research is available

Review conclusions are probably dated

Update decision

Based on the above criteria, the decision is made to either update, archive, or continue surveillance.

Of over 50 Cochrane editorial teams, most but not all have some systems for updating, although this process can be informal and loosely applied. Most editorial teams draw on some or all of the following criteria:

Strategic importance

Is the topic a priority area (for example, in current debates or considered by guidelines groups)?

Is there important new information available?

Practicalities in organising the update that many groups take into account

Size of the task (size and quality of the review, and how many new studies or analyses are needed)

Availability and willingness of the author team

Impact of update

New research impact on findings and credibility

Consider whether new methods will improve review quality

Priority to update, postpone update, class review as no longer requiring an update

The PUGs panel recommended an individualised approach to updating, which used the procedures summarised in figure 1 ⇓ . The figure provides a status category, and some options for classifying reviews into each of these categories, and builds on a previous decision tool and earlier work developing an updating classification system. 15 16 We provide a narrative for each step.

Fig 1 Decision framework to assess systematic reviews for updating, with standard terms to report such decisions

Step 1: assess currency

Does the published review still address a current question.

An update is only worthwhile if the question is topical for decision making for practice, policy, or research priorities (fig 1 ⇑ ). For agencies, people responsible for managing a portfolio of systematic reviews, there is a need to use both formal and informal horizon scanning. This type of scanning helps identify questions with currency, and can help identify those reviews that should be updated. The process could include monitoring policy debates around the review, media outlets, scientific (and professional) publications, and linking with guideline developers.

Has the review had good access or use?

Metrics for citations, article access and downloads, and sharing via social or traditional media can be used as proxy or indicators for currency and relevance of the review. Reviews that are widely cited and used could be important to update should the need arise. Comparable reviews that are never cited or rarely downloaded, for example, could indicate that they are not addressing a question that is valued, and might not be worth updating.

In most cases, updated reviews are most useful to stakeholders when there is new information or methods that result in a change in findings. However, there are some circumstances in which an up to date search for information is important for retaining the credibility of the review, regardless of whether the main findings would change or not. For example, key stakeholders would dismiss a review if a study is carried out in a relevant geographical setting but is not included; if a large, high profile study that might not change the findings is not included; or if an up to date search is required for a guideline to achieve credibility. Box 3 provides such examples. If the review does not answer a current question, the intervention has been superseded, then a decision can be made not to update and no further intelligence gathering is required (fig 1 ⇑ ).

Box 3: Examples of a systematic review’s currency

The public is interested in vitamin C for preventing the common cold: the Cochrane review includes over 29 trials with either no or small effects, concluding good evidence of no important effects. 17 Assessment: still a current question for the public.

Low osmolarity oral rehydration salt (ORS) solution versus standard solution for acute diarrhoea in children: the 2001 Cochrane review 18 led the World Health Organization to recommend ORS solution formula worldwide to follow the new ORS solution formula 19 and this has now been accepted globally. Assessment: no longer a current question.

Routine prophylactic antibiotics with caesarean section: the Cochrane review reports clear evidence of maternal benefit from placebo controlled trials but no information on the effects on the baby. 20 Assessment: this is a current question.

A systematic review published in the Lancet examined the effects of artemisinin based combination treatments compared with monotherapy for treating malaria and showed clear benefit. 21 Assessment: this established the treatment globally and is no longer a current question and no update is required.

A Cochrane review of amalgam restorations for dental caries 22 is unlikely to be updated because the use of dental amalgam is declining, and the question is not seen as being important by many dental specialists. Assessment: no longer a current question.

Did the review use valid methods and was it well conducted?

If the question is current and clearly defined, the systematic review needs to have used valid methods and be well conducted. If the review has vague inclusion criteria, poorly articulated outcomes, or inappropriate methods, then updating should not proceed. If the question is current, and the review has been cited or used, then it might be appropriate to simply start with a new protocol. The appraisal should take into account the methods in use when the review was done.

Step 2: identify relevant new methods, studies, and other information

Are there any new relevant methods.

If the question is current, but the review was done some years ago, the quality of the review might not meet current day standards. Methods have advanced quickly, and data extraction and understanding of the review process have become more sophisticated. For example:

Methods for assessing risk of bias of randomised trials, 23 diagnostic test accuracy (QUADAS-2), 24 and observational studies (ROBINS-1). 25

Application of summary of findings, evidence profiles, and related GRADE methods has meant the characteristics of the intervention, characteristics of the participants, and risk of bias are more thoroughly and systematically documented. 26 27

Integration of other study designs containing evidence, such economic evaluation and qualitative research. 28

There are other incremental improvements in a wide range of statistical and methodological areas, for example, in describing and taking into account cluster randomised trials. 29 AMSTAR can assess the overall quality of a systematic review, 30 and the ROBIS tool can provide a more detailed assessment of the potential for bias. 31

Are there any new studies or other information?

If an authoring or commissioning team wants to ensure that a particular review is up to date, there is a need for routine surveillance for new studies that are potentially relevant to the review, by searching and trial register inspection at regular intervals. This process has several approaches, including:

Formal surveillance searching 32

Updating the full search strategies in the original review and running the searches

Tracking studies in clinical trial and other registers

Using literature appraisal services 33

Using a defined abbreviated search strategy for the update 34

Checking studies included in related systematic reviews. 35

How often this surveillance is done, and which approaches to use, depend on the circumstances and the topic. Some topics move quickly, and the definition of “regular intervals” will vary according to the field and according to the state of evidence in the field. For example, early in the life of a new intervention, there might be a plethora of studies, and surveillance would be needed more frequently.

Step 3: assess the effect of updating the review

Will the adoption of new methods change the findings or credibility.

Editors, referees, or experts in the topic area or methodologists can provide an informed view of whether a review can be substantially improved by application of current methodological expectations and new methods (fig 1 ⇑ ). For example, a Cochrane review of iron supplementation in malaria concluded that there was “no significant difference between iron and placebo detected.” 36 An update of the review included a GRADE assessment of the certainty of the evidence, and was able to conclude with a high degree of certainty that iron does not cause an excess of clinical malaria because the upper relative risk confidence intervals of harm was 1.0 with high certainty of evidence. 37

Will the new studies, information, or data change the findings or credibility?

The assessment of new data contained in new studies and how these data might change the review is often used to determine whether an update should go ahead, and the speed with which the update should be conducted. The appraisal of these new data can be carried out in different ways. Initially, methods focused on statistical approaches to predict an overturning of the current review findings in terms of the primary or desired outcome (table 1 ⇓ ). Although this aspect is important, additional studies can add important information to a review, which is more than just changing the primary outcome to a more accurate and reliable estimate. Box 4 gives examples.

Formal prediction tools: how potentially relevant new studies can affect review conclusions

Box 4: Examples of new information other than new trials being important

The iconic Cochrane review of steroids in preterm labour was thought to provide evidence of benefit in infants, and this question no longer required new trials. However, a new large trial published in the Lancet in 2015 showed that in low and middle income countries, strategies to promote the uptake of neonatal steroids increased neonatal mortality and suspected maternal infection. 49 This information needs to somehow be incorporated into the review to maintain its credibility.

A Cochrane review of community deworming in developing countries indicates that in recent studies, there is little or no effect. 50 The inclusion of a large trial of two million children confirmed that there was no effect on mortality. Although the incorporation of the trial in the review did not change the review’s conclusions, the trial’s absence would have affected the credibility of the review, so it was therefore updated.

A new paper reporting long term follow-up data on anthracycline chemotherapy as part of cancer treatment was published. Although the effects from the outcomes remained essentially unchanged, apart from this longer follow-up, the paper also included information about the performance bias in the original trial, shifting the risk of bias for several outcomes from “unknown” to “high” in the Cochrane review. 51

Reviews with a high level of certainty in the results (that is, when the GRADE assessment for the body of evidence is high) are less likely to change even with the addition of new studies, information, or data, by definition. GRADE can help guide priorities in whether to update, but it is still important to assess new studies that might meet the inclusion criteria. New studies can show unexpected effects (eg, attenuation of efficacy) or provide new information about the effects seen in different circumstances (eg, groups of patients or locations).

Other tools are specifically designed to help decision making in updating. For example, the Ottawa 39 and RAND 45 methods focus on identification of new evidence, the statistical predication tool 15 calculates the probability of new evidence changing the review conclusion, and the value of information analysis approach 52 calculates the expected health gain (table 1 ⇑ ). As yet, there has been limited external validation of these tools to determine which approach would be most effective and when.

If potentially relevant studies are identified that have not previously been assessed for inclusion, authors or those managing the updating process need to assess whether including them might affect the conclusions of the review. They need to examine the weight and certainty of the new evidence to help determine whether an update is needed and how urgent that update is. The updating team can assess this informally by judging whether new studies or data are likely to substantively affect the review, for example, by altering the certainty in an existing comparison, or by generating new comparisons and analyses in the existing review.

New information can also include fresh follow-up data on existing included studies, or information on how the studies were carried out. These should be assessed in terms of whether they might change the review findings or improve its credibility (fig 1 ⇑ ). Indeed, if any study has been retracted, it is important the authors assess the reasons for its retraction. In the case of data fabrication, the study needs to be removed from the analysis and this recorded. A decision needs to be made as to whether other studies by the same author should be removed from the review and other related reviews. An investigation should also be initiated following guidelines from the Committee on Publication Ethics (COPE). Additional published and unpublished data can become available from a wide range of sources—including study investigators, regulatory agencies and industry—and are important to consider.

Preparing for an update

Refresh background, objectives, inclusion criteria, and methods

Before including new studies in the review, authors need to revisit the background, objectives, inclusion criteria, and methods of the current review. In Cochrane, this is referred to as the protocol, and editors are part of this process. The update could range from simply endorsing the current question and inclusion criteria, through to full rewriting of the question, inclusion criteria and methods, and republishing the protocol. As a field progresses with larger and better quality trials rigorously testing the questions posed, it may be appropriate to exclude weaker study designs (such as quasi-randomised comparisons or very small trials) from the update (table 2 ⇓ ). The PUGs panel recommended that a protocol refresh will require the authors to use the latest accepted methods of synthesis, even if this means repeating data extraction for all studies.

New authors and authorship

Updated systematic reviews are new publications with new citations. An authorship team publishing an update in a scientific or medical journal is likely to manage the new edition of a review in the same way as with any other publication, and follow the ICMJE authorship criteria. 56 If the previous author or author team steps down, then they should be acknowledged in the new version. However, some might perceive that their efforts in the first version warrant continued authorship, which may be valid. The management of authorship between versions can sometimes be complicated. At worst, it delays new authors completing an update and leads to long authorship lists of people from previous versions who probably do not meet ICMJE authorship criteria. One approach with updates including new authors is to have an opt-in policy for the existing authors: they can opt in to the new edition, provided that they make clear their contribution, and this is then agreed with the entire author team.

Although they are new publications, updates will generally include content from the published version. Changing licensing rights around systematic reviews to allow new authors of future updates to remix, tweak, or build on the contributions of the original authors of the published version (similar to the rights available via a Creative Commons licence; https://creativecommons.org ) could be a more sustainable and simpler approach. This approach would allow systematic reviews to continue to evolve and build on the work of a range of authors over time, and for contributors to be given credit for contributions to this previous work.

Efficient searching

In performing an update, a search based on the search conducted for the original review is required. The updated search strategy will need to take into account changes in the review question or inclusion criteria, for example, and might be further adjusted based on knowledge of running the original search strategy. The search strategy for an update need not replicate the original search strategy, but could be refined, for example, based on an analysis of the yield of the original search. These new search approaches are currently undergoing formal empirical evaluation, but they may well provide much more efficient search strategies in the future. Some examples of these possible new methods for review updates are described in web appendix 2.

In reporting the search process for the update, investigators must ensure transparency for any previous versions and the current update, and use an adapted flow diagram based on PRISMA reporting (preferred reporting items for systematic reviews and meta-analyses). 57 The search processes and strategies for the update must be adequately reported such that they could be replicated.

Systematic reviews published for the first time in peer reviewed journals are by definition peer reviewed, but practice for updates remains variable, because an update might have few changes (such as an updated search but no new studies found and therefore included) or many changes (such as revise methods and inclusion of several new studies leading to revised conclusions). Therefore, and to use peer reviewers’ time most effectively, editors need to consider when to peer review an update and the type of peer reviewer most useful for a particular update (for example, topic specialist, methodologist). The decision to use peer review, and the number and expertise of the peer reviewers could depend on the nature of the update and the extent of any changes to the systematic review as part of an editor assessment. A change in the date of the search only (where no new studies were identified) would not require peer review (except, arguably, peer review of the search), but the addition of studies that lead to a change in conclusions or significant changes to the methods would require peer review. The nature of the peer review could be described within the published article.

Reporting changes

Authors should provide a clear description of the changes in approach or methods between different editions of a review. Also, authors need to report the differences in findings between the original and updated edition to help users decide how to use the new edition. The approach or format used to present the differences in findings might vary with the target user group. 58 Publishers need to ensure that all previous versions of the review remain publically accessible.

Updates can range from small adjustments to reviews being completely rewritten, and the PUGs panel spent some time debating whether the term “new edition” would be a better description than “update.” However, the word “update” is now in common parlance and changing the term, the panel judged, could cause confusion. However, the debate does illustrate that an update could represent a review that asks a similar question but has been completely revised.

Technology and innovation

The updating of systematic review is generally done manually and is time consuming. There are opportunities to make better use of technology to streamline the updating process and improve efficiency (table 3 ⇓ ). Some of these tools already exist and are in development or in early use, and some are commercially available or freely available. The AHRQ’s evidence based practice centre team has recently published tools for searching and screening, and will provide an assessment of the use, reliability, and availability of these tools. 63

Technological innovations to improve the efficiency of updating systematic reviews

Other developments, such as targeted updates that are performed rapidly and focus on updating only key components of a review, could provide different approaches to updating in the future and are being piloted and evaluated. 64 With implementation of these various innovations, the longer term goal is for “living” systematic reviews, which identify and incorporate information rapidly as it evolves over time. 60

Concluding remarks

Updating systematic reviews, rather than addressing the same question with a fresh protocol, is generally more efficient and allows incremental improvement over time. Mechanical rules appear unworkable, but there is no clear unified approach on when to update, and how implement this. This PUGs panel of authors, editors, statisticians, information specialists, other methodologists, and guideline developers brought together current thinking and experience in this area to provide guidance.

Decisions about whether and when to update a systematic review are judgments made at a point in time. They depend on the currency of the question asked, the need for updating to maintain credibility, the availability of new evidence, and whether new research or new methods will affect the findings.

Whether the review uses current methodological standards is important in deciding if the update will influence the review findings, quality, reliability, or credibility sufficiently to justify the effort in updating it. Those updating systematic reviews to author clinical practice guidelines might consider the influence of new study results in potentially overturning the conclusions of an existing review. Yet, even in cases where new study findings do not change the primary outcome measure, new studies can carry important information about subgroup effects, duration of treatment effects, and other relevant clinical information, enhancing the currency and breadth of review results.

An update requires appraisal and revision of the background, question, inclusion criteria, and methods of the existing review and the existing certainty in the evidence. In particular, methods might need to be updated, and search strategies reconsidered. Authors of updates need to consider inputs to the current edition, and follow ICMJE criteria regarding authorship. 56

The PUGs panel proposed a decision framework (fig 1 ⇑ ), with terms and categories for reporting the decisions made for updating procedures for adoption by Cochrane and other stakeholders. This framework includes journals publishing systematic review updates and independent authors considering updates of existing published reviews. The panel developed a checklist to help judgements about when and how to update.

The current emphasis of authors, guideline developers, Cochrane, and consequently this guidance has been on effects reviews. The checklists and guidance here still applies to other types of systematic reviews, such as those on diagnostic test accuracy, and this guidance will need adapting. Accumulative experience and methods development in reviews other than those of effects are likely to help refine guidance in the future.

This guidance could help groups identify and prioritise reviews for updating and hence use their finite resources to greatest effect. Software innovation and new management systems are being developed and in early use to help streamline review updates in the coming years.

Contributors: HJS initiated the workshop. JC, SH, PG, HM, and HJS organised the materials and the agenda. SH wrote up the proceedings. PG wrote the paper from the proceedings and coordinated the development of the final guidance; JC, SH, HM, and HJS were active in the finalising of the guidance. All PUGs authors contributed to three rounds of manuscript revision.

Funding: Attendance at this meeting, for those attendees not directly employed by Cochrane, was not funded by Cochrane beyond the reimbursement of out of pocket expenses for those attendees for whom this was appropriate. Expenses were not reimbursed for US federal government attendees, in line with US government policy. Statements in the manuscript should not be construed as endorsement by the US Agency for Healthcare Research and Quality or the US Department of Health and Human Services.

Competing interests: All participants have a direct or indirect interest in systematic reviews and updating as part of their job or academic career. Most participants contribute to Cochrane, whose mission includes a commitment to the updating of its systematic review portfolio. JC, HM, RM, CM, KS-W, and MT are, or were at that time, employed by the Cochrane Central Executive.

Provenance and peer review: Not commissioned; externally peer reviewed.

This is an Open Access article distributed in accordance with the terms of the Creative Commons Attribution (CC BY 3.0) license, which permits others to distribute, remix, adapt and build upon this work, for commercial use, provided the original work is properly cited. See: http://creativecommons.org/licenses/by/3.0/ .

an updated review of the literature

Conduct a literature review

What is a literature review.

A literature review is a summary of the published work in a field of study. This can be a section of a larger paper or article, or can be the focus of an entire paper. Literature reviews show that you have examined the breadth of knowledge and can justify your thesis or research questions. They are also valuable tools for other researchers who need to find a summary of that field of knowledge.

Unlike an annotated bibliography, which is a list of sources with short descriptions, a literature review synthesizes sources into a summary that has a thesis or statement of purpose—stated or implied—at its core.

How do I write a literature review?

Step 1: define your research scope.

Ask us if you have questions about refining your topic, search methods, writing tips, or citation management.

Step 2: Identify the literature

Start by searching broadly. Literature for your review will typically be acquired through scholarly books, journal articles, and/or dissertations. Develop an understanding of what is out there, what terms are accurate and helpful, etc., and keep track of all of it with citation management tools . If you need help figuring out key terms and where to search, ask us .

Use citation searching to track how scholars interact with, and build upon, previous research:

Step 3: Critically analyze the literature

Key to your literature review is a critical analysis of the literature collected around your topic. The analysis will explore relationships, major themes, and any critical gaps in the research expressed in the work. Read and summarize each source with an eye toward analyzing authority, currency, coverage, methodology, and relationship to other works. The University of Toronto's Writing Center provides a comprehensive list of questions you can use to analyze your sources.

Step 4: Categorize your resources

Divide the available resources that pertain to your research into categories reflecting their roles in addressing your research question. Possible ways to categorize resources include organization by:

Regardless of the division, each category should be accompanied by thorough discussions and explanations of strengths and weaknesses, value to the overall survey, and comparisons with similar sources. You may have enough resources when:

Additional resources

Undergraduate student resources.

Graduate student and faculty resources

Graustein, J. S. (2012). How to Write an Exceptional Thesis or Dissertation: A Step-by-Step Guide from Proposal to Successful Defense [ebook]

Thomas, R. M. & Brubaker, D. L. (2008). Theses and Dissertations: A Guide to Planning, Research, and Writing


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    Universitat Rovira i Virgili, Laboratory of Toxicology and Environmental Health, School of Medicine, 43201, Reus, Catalonia, Spain. Electronic

  3. Early Childhood Educators' Well-Being: An Updated Review of the

    also identified some specific problems with the body of literature that they reviewed: the small number of data-driven, peer-reviewed research

  4. The mass customization decade: An updated review of the literature

    Mass customization: literature review and research directions. International Journal of Production Economics, 72 (1), 1–13), and identify research gaps to be

  5. The nature of labour pain: An updated review of the literature

    Aim. To provide an update of our understanding of labour pain based on modern pain science. The review aims to help explain why women can experience labour

  6. Homophobia: An updated review of the literature.

    This paper updates the literature review on homophobia revisiting society's assumptions about homosexuals. Changes are discussed in the context of

  7. Gulf War and Health: Updated Literature Review of Sarin

    Institute of Medicine. 2004. Gulf War and Health: Updated Literature Review of Sarin. Washington, DC: The National Academies Press. https://doi.org/10.17226/

  8. Literature Reviews

    The main focus of an academic research paper is to develop a new argument, and a research paper is likely to contain a literature review as one of its parts

  9. When and how to update systematic reviews: consensus and checklist

    Citation in scientific literature including clinical practice guidelines. Currency and need for update. New research is available. Review

  10. Conduct a literature review

    This can be a section of a larger paper or article, or can be the focus of an entire paper. Literature reviews show that you have examined the breadth of