The Importance of Systematic Reviews

In the following step, Jayne Wilson, a senior systematic reviewer in the systematic review team at the Cancer Research UK Clinical Trials Unit at Birmingham University explains why systematic reviews are so important before embarking on a trial. Is there a gap in the evidence? Are we really in clinical equipoise?

Systematic reviews reduce unwanted duplication of research, help ensure that new research builds on lessons from earlier research and places the findings of the new research into proper context - Mark Clarke, 2007

Health professionals are required to use all available evidence when making decisions about the care of a patient. However, relevant evidence for a specific clinical question, from published and ongoing studies, is often extensive and contradictory. How can sense be made of all this evidence? How can it be amalgamated to best inform clinical practice?

Systematic reviews and meta analyses aim to identify, evaluate, and summarise the findings of all individual studies relevant to a specific question. Such reviews make the wealth of information more manageable and accessible to policy makers and healthcare professionals. Systematic reviews and meta analyses are also essential for those working within clinical trials, to inform the need or rationale, and the design of future trials.

During this step, Jayne talked about a study conducted by Fergusson and colleagues which illustrated how, sometimes, trials are conducted for a specific research question that has already been answered by previous trials. For more information on this study, see: Fergusson, D., Glass, K.C., Hutton, B., & Shapiro, S. 2005. Randomized controlled trials of aprotinin in cardiac surgery: could clinical equipoise have stopped the bleeding? Clinical Trials, 2, (3) 218-229.

Of course, the importance of systematic reviews and meta analyses comes with the caveat that they must be both well conducted and reported, so that they offer an unbiased, comprehensive assessment of current evidence.

Registration of systematic reviews

All systematic reviews should be registered on PROSPERO (https://www.crd.york.ac.uk/prospero/), an International prospective register of systematic reviews within healthcare, public health and social care and other research areas. Registration helps avoid duplication of effort and alert the research community that a systematic review, in a specific area, is in progress.

If protocols of planned systematic reviews are registered at inception this also reduces any opportunity for reporting bias by enabling comparison of the completed review with what was planned in the protocol.

Reporting guidelines

When writing up a systematic review or meta-analysis, authors should follow the Preferred Reporting Guidelines for Systematic Reviews and Meta-Analyses (PRISMA) (http://www.prisma-statement.org/). These guidelines contain the minimum set of items that should be reported by all authors and covers the rationale for the review, the methods used and the results. Accordance with the guidelines ensures consistency across reporting of reviews and transparency of methods.

It is also important however, that the results of our trial are used to update any existing systematic review and meta-analysis in the relevant research area. It is important, therefore, for clinical trial staff to be aware of the processes involved in conducting a systematic review and meta-analysis.

Finding published systematic reviews

You might not always need to do your own systematic review ahead of planning your trial. You should always start by searching for a published review that is relevant to your trial. We can find systematic reviews in a variety of places in addition to bibliographic databases. Below is a list where you can find further information.

Critical appraisal of published systematic reviews

There are several checklists, which can help you read and critically appraise published systematic reviews. These include the Critical Appraisal Skills Programme (CASP) and AMSTAR (A MeaSurement Tool to Assess systematic Reviews), links to these tools are provided below.

Additional Resources

International prospective register of systematic reviews: https://www.crd.york.ac.uk/prospero/
Reporting guidelines for systematic reviews and meta-analyses (PRISMA): https://www.prisma-statement.org/
Cochrane Library: https://www.cochranelibrary.com/
The National Institute for Health Research: https://www.journalslibrary.nihr.ac.uk/journals
National Institute for Health and Care Research: https://www.journalslibrary.nihr.ac.uk/journals
Health Technology Assessment International: https://htai.org/
The Canadian Agency for Drugs and Technologies in Health: https://www.cda-amc.ca/
TRIP: https://www.tripdatabase.com/
Aggressive Research Intelligence Facility: https://s4be.cochrane.org/blog/2013/02/13/arif-reviews-database/
Epistemonikos: https://www.epistemonikos.org/
Systematic Review Center for Laboratory Animal Experimentation: https://syrcle.network/
Critical Appraisal Skills Programme: https://casp-uk.net/casp-tools-checklists/
A Measurement tool to assess systematic reviews: https://amstar.ca/Amstar_Checklist.php

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