Study within a review (SWAR)

Systematic reviews and other evidence syntheses bring together information from multiple studies to help inform policy and practice decisions. They use systematic methods to identify, select, appraise (where appropriate), and analyze a body of evidence and report their findings with the aim of minimizing bias and helping people make well-informed decisions. Alongside the enormous increase in the number of systematic reviews,1, 2 recent decades have witnessed prodigious growth in the evidence base to inform decisions on how we plan, do and share the findings of systematic reviews.3 For example, methodological papers and consensus statements on the development and validation of search strategies, assessment of the risk of bias, synthesis of complex interventions, qualitative evidence synthesis, etc., regularly appear in peer-reviewed journals.4-7

This evolving evidence base on how we plan, do, and share the findings of reviews is important, relevant and helpful. However, many evidence uncertainties exist and greater efforts, ideally in a coordinated manner, are needed to address them across the systematic review process. Examples include optimal approaches to searching and citation screening,8 the effectiveness of machine learning in supporting screening and/or data extraction,9 and the effectiveness of different modes of sharing the findings of reviews with different audiences.10 In addition, developments in systematic review approaches need high-quality evidence to inform decisions about how they are done. For example, living systematic reviews, which seek to reduce the time between the availability of the findings of primary research studies and their synthesis, need better evidence to inform decisions around team processes, managing workloads, integration of pathways from searching and screening through data extraction to updating analyses.11 These uncertainties will persist unless the evaluation of alternative approaches to review processes becomes commonplace. A resource-efficient way of conducting these evaluations is to undertake a Study Within A Review (SWAR). A SWAR is a discrete study analogous to the Study Within A Trial (SWAT), which aims to strengthen the evidence base for trial methods.12 A SWAR and SWAT registry was established by the All-Ireland Hub for Trials Methodology Research (now the Northern Ireland Methodology Hub) in collaboration with the Medical Research Council's Network of Hubs in the UK and the Global Health Network.13 The registries are available for researchers across the globe to register outlines for their SWAR and SWAT at no charge and are free to view (go.qub.ac.uk/SWAT-SWAR).

This paper aims to describe SWARs, highlight their importance, and discuss key considerations for conducting a SWAR. This will help systematic reviewers, funders, those mining the evidence base, and methodologists to plan, conduct, or support studies to improve the evidence base of systematic review and evidence synthesis methods. Researchers generally make the decision to conduct a SWAR: we hope this paper will convince more researchers to include one in their reviews.