4: Different types of reviews
The number of health-related reviews has grown enormously over recent decades, showing how useful this way of synthesising the research literature can be. Over this time, several types of reviews have been developed as review methods have been applied to different health questions and problems. As this has occurred in different places, in different disciplines and for different reasons, a range of names have been applied for review types that have been created.
One group of information specialists (or librarians) identified 48 distinct review types, which they categorised into seven broad review ‘families’:[1]
- Traditional reviews
- Systematic reviews
- Rapid reviews
- Overviews (reviews of reviews)
- Qualitative reviews
- Purpose-specific reviews (scoping reviews)
- Mixed methods reviews
These many types of reviews have developed in response to the range of questions that can be answered by research studies. While the number of different types of reviews may seem overwhelming, they reflect the range of questions that arise in health care and in the development of health policy. Moreover, there are generic skills common to most review types, and this book focuses on these.
We will use the framework from Sutton and colleagues to briefly describe the different types of reviews. Then we will look at some of the skills you need to conduct a high-quality review – of any type.
Further reading
For more detail about the review framework, read the full paper by Sutton and colleagues.
Meeting the review family: exploring review types and associated information retrieval requirements
Traditional reviews
Traditional reviews have been around for many years; they provide summaries of research on particular topics. This family includes reviews described as critical or integrative and provides a more conventional or narrative exploration of the literature. Until recently, this group of reviews has mostly not included detailed descriptions of methods used, although this is changing and greater transparency is increasingly common.
Example
This traditional review summarised studies looking at changes in dietary consumption reported in European populations from 1990 to 2020.[2]
Nutrition transition in Europe: East–west dimensions in the last 30 years – a narrative review
Systematic reviews
Systematic reviews in health care underpin the concept of evidence-based practice by reinforcing the value of systematic approaches to synthesising research evidence. Their purpose is to summarise the available evidence in existing research based on a comprehensive search of the literature to answer specific questions related to health issues. The term ‘systematic review’ has been used somewhat loosely for several years to cover any review using a systematic approach. More recently there has been a marked shift to tighter use of the terminology.
Systematic reviews that seek to establish the effectiveness of different treatments or interventions essentially ask ‘Does this work?’ Cochrane reviews are considered the gold standard for effectiveness reviews, particularly for clinical questions, as they follow formal guidance that requires a published protocol, extensive search strategies and a very high level of transparency. These reviews are held in the Cochrane Database of Systematic Reviews (CDSR) and cover a range of health topics. Cochrane reviews can be very time-consuming, with many taking years to complete.
The development of systematic reviews raised awareness of the usefulness of reviews to health decision-making. Before the 1980s there were relatively few systematic reviews in health care, but now more than 10,000 systematic reviews are published every year, including those in the CDSR.[3] Not all of these will influence healthcare practice, but many reviews have had a big impact on the provision of care.
Since the rise in importance of systematic reviews, the range of review types has grown based on similar methodological approaches as those used in systematic reviews.[4]
Other reviews in the systematic review family are economic evaluations and diagnostic test accuracy reviews. While these are important, they are outside the scope of this book.
Examples
Cochrane reviews have changed the practice of medicine internationally. This review,[5] the first version of which was published in 1998, supported the use of a single course of steroids for women at risk of pre-term birth, significantly improving the survival rate of babies born prematurely.
Antenatal corticosteroids for accelerating fetal lung maturation for women at risk of preterm birth
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Systematic reviews are sometimes referred to as meta-analysis, which, strictly speaking, is the statistical process used to combine results from similar studies. However, not all systematic reviews include a meta-analysis, for various reasons.
The next review[6] (without a meta-analysis) looked at mobile apps during pregnancy. The authors could not draw any conclusions due to the wide range of approaches used in the original studies. These varied in terms of how participants and the interventions were described, and the types of outcomes measured. Instead, the authors drew attention to this important limitation and recommended that a standardised approach be developed to allow comparison.
Rapid reviews
Rapid reviews have been increasingly seen in recent years. These essentially use an abridged version of the methods of a full systematic review to speed up the review timeline to meet the specific needs of the commissioning agent or institution. For example, several rapid reviews were conducted in response to the COVID-19 pandemic, to meet the emergency responses needed in policy and practice. Like systematic reviews, rapid reviews should start with a protocol or plan. Changes to that plan during the conduct of the rapid review, including any identified limitations, must be clearly stated in the final report.
Example
This rapid review[7] looked at the impact of the COVID-19 pandemic in studies of cancer survivors in rural areas. It included 14 studies using different study designs reporting patient experiences to inform the development of future support interventions.
Overviews
Overviews – or reviews of reviews – are another offshoot of the rapid growth in systematic reviews. Overviews use similar search and report approaches to systematic reviews but, rather than looking at primary studies, aim to summarise existing reviews on the same topic. One common alternative name for overviews is ‘umbrella’ reviews.
The development of overviews has only been possible with the growth in the number of reviews available. In an overview, it is important to check for any overlap between the included reviews (i.e. whether the same studies have been used) so that findings are not unintentionally magnified.
Example
This overview[8] looked at health service use by refugees.
Qualitative reviews
Reviews of qualitative studies are less established in the literature compared with those that aim to synthesise the findings of quantitative studies; however, these reviews are growing rapidly in terms of numbers and the approaches used. Among the many names used to describe qualitative reviews, ‘qualitative meta-synthesis’ is possibly the most common.
Qualitative reviews aim to either aggregate findings from a range of studies or interpret findings in new ways – for example, by framing a question differently. In doing so they develop or test new theoretical perspectives. Qualitative reviews can also be used to explore existing theories or to identify issues for future studies or services to address.
Examples
A review by Carlsen and Glenton[9] sought to explore public attitudes to swine flu vaccines. The review authors raised questions about the conclusions drawn by the authors of the original studies and offered an alternative conclusion that could be drawn from the evidence provided in the studies.
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Ikpeme and colleagues[10] sought to identify inequalities in work-life balance for vets and allied professionals.
Work-life balance inequalities among veterinary and allied professionals: A qualitative review
Purpose-specific reviews (scoping reviews)
Purpose-specific reviews – Sutton and colleagues call them scoping reviews – aim to identify the type and extent of existing research literature on a topic.
‘Scoping reviews’ are comprised of reviews that include a range of heterogenous studies. Such reviews are commonly designed for a specific purpose, so can also be referred to as purpose specific reviews. The amount of tailoring needed to meet a specific single purpose makes it difficult to adapt this review type for generic use.[11]
For some reviews in this family there can be formal guidance on how to approach the review. For example, scoping reviews, and their close relative mapping reviews, aim to identify existing research related to a question or topic to find potential gaps where future research is needed. Many of the skills used in systematic reviews are also used in purpose-specific reviews.
Example
This review[12] examined public involvement in human genomics research projects in terms of what it looks like, how it happens and what the impacts have been.
Public involvement in global genomics research: A scoping review
Mixed methods reviews
As the name implies, a mixed methods review aims to integrate studies that include quantitative and qualitative data. Some reviews in this family include only mixed methods studies or studies involving the same study population, whereas others will incorporate studies looking at effectiveness (quantitative studies), associated costs (economic evaluations), the experiences of people with the health condition or those who have been subject to or participated in an intervention, such as an education program or clinical investigation.
Examples
Katrak and colleagues[13] looked at the content of critical appraisal tools. They concluded that there was no gold standard for appraisal and that tools should be selected based on the needs of the review question.
A systematic review of the content of critical appraisal tools
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Williams and colleagues used a mixed methods approach[14] to address an anticipated shortage of research in order to find out what was known about the effectiveness of loneliness and social isolation interventions in rural adult communities.
Interventions to reduce loneliness and social isolation in rural settings: A mixed-methods review
- Sutton, A., Clowes, M., Preston, L., & Booth, A. (2019). Meeting the review family: Exploring review types and associated information retrieval requirements. Health Information & Libraries Journal, 36(3), 202–222. https://doi.org/10.1111/hir.12276 ↵
- Dokova, K. G., Pancheva, R. Z., Usheva, N.V., Haralanova, G. A., Nikolova, S. P., Kostadinova, T. I., Egea Rodrigues, C., Singh, J., Illner, A-K., & Aleksandrova, K. (2022). Nutrition transition in Europe: East–west dimensions in the last 30 years – a narrative review. Frontiers in Nutrition, 9, 919112. https://doi.org/10.3389/fnut.2022.919112 ↵
- Clarke, M., & Chalmers, I. (2018). Reflections on the history of systematic reviews. BMJ Evidence-Based Medicine, 23(4), 121–122. http://dx.doi.org/10.1136/bmjebm-2018-110968 ↵
- See Clarke and Chalmers (2018). ↵
- Roberts, D., Brown, J., Medley, N., & Dalziel, S. R. (2017). Antenatal corticosteroids for accelerating fetal lung maturation for women at risk of preterm birth. Cochrane Database of Systematic Reviews, 3. https://doi.org/10.1002/14651858.CD004454.pub4 ↵
- Daly, L., Horey, D., Middleton, P., Boyle, F., & Flenady, V. (2018). The effect of mobile app interventions on influencing healthy maternal behavior and improving perinatal health outcomes: Systematic review. JMIR mHealth and uHealth, 6(8), e10012. DOI: https://doi.org/10.2196/10012 ↵
- Nelson, D., Cooke, S., McLeod, B., Nanyonjo, A., Kane, R., & Gussy, M. (2022). A rapid systematic review on the experiences of cancer survivors residing in rural areas during the COVID-19 pandemic. International Journal of Environmental Research and Public Health,19(24), 16863. https://doi.org/10.3390/ijerph192416863 ↵
- Parajuli, J., & Horey, D. (2019). Barriers to and facilitators of health services utilisation by refugees in resettlement countries: An overview of systematic reviews. Australian Health Review, 44(1), 132–142. https://doi.org/10.1071/ah18108 ↵
- Carlsen, B., & Glenton, C. (2016). The swine flu vaccine, public attitudes, and researcher interpretations: A systematic review of qualitative research. BMC Health Services Research, 16(1), 1. https://doi.org/10.1186/s12913-016-1466-7 ↵
- Ikpeme, M., Omotoyinbo, F., Toluwade, T., & Ryan, M. (2021). Work-life balance inequalities among veterinary and allied professionals: A qualitative review. European Journal of Public Health, 31(Supplement_3), ckab165-328. https://doi.org/10.1093/eurpub/ckab165.328 ↵
- Sutton, A., Clowes, M., Preston, L., & Booth, A. (2019). Meeting the review family: Exploring review types and associated information retrieval requirements. Health Information & Libraries Journal, 36(3), 202–222. https://doi.org/10.1111/hir.12276 ↵
- Nunn, J. S., Tiller, J., Fransquet, P., & Lacaze, P. (2019). Public involvement in global genomics research: A scoping review. Frontiers in Public Health, 79. https://doi.org/10.3389/fpubh.2019.00079 ↵
- Katrak, P., Bialocerkowski, A. E., Massy-Westropp, N., Kumar, V. S., & Grimmer, K. A. (2004). A systematic review of the content of [pb_glossary id="185"]critical appraisal[/pb_glossary] tools. BMC Medical Research Methodology, 4(1), 1. https://doi.org/10.1186/1471-2288-4-22 ↵
- Williams, T., Lakhani, A., & Spelten, E. (2022). Interventions to reduce loneliness and social isolation in rural settings: A mixed-methods review. Journal of Rural Studies, 90, 76–92. https://doi.org/10.1016/j.jrurstud.2022.02.001 ↵
Benchmark for best practice.
Use of statistical methods to combine data from studies included in a systematic review. https://latrobe.libguides.com/systematicreviews
Detailed plan for study, or review, to be undertaken.
