Abstract
BackgroundSystematic reviews of qualitative and quantitative evidence can provide a rich understanding of complex phenomena. This type of review is increasingly popular, has been used to provide a landscape of existing knowledge, and addresses the types of questions not usually covered in reviews relying solely on either quantitative or qualitative evidence. Although several typologies of synthesis designs have been developed, none have been tested on a large sample of reviews. The aim of this review of reviews was to identify and develop a typology of synthesis designs and methods that have been used and to propose strategies for synthesizing qualitative and quantitative evidence.MethodsA review of systematic reviews combining qualitative and quantitative evidence was performed. Six databases were searched from inception to December 2014. Reviews were included if they were systematic reviews combining qualitative and quantitative evidence. The included reviews were analyzed according to three concepts of synthesis processes: (a) synthesis methods, (b) sequence of data synthesis, and (c) integration of data and synthesis results.ResultsA total of 459 reviews were included. The analysis of this literature highlighted a lack of transparency in reporting how evidence was synthesized and a lack of consistency in the terminology used. Two main types of synthesis designs were identified: convergent and sequential synthesis designs. Within the convergent synthesis design, three subtypes were found: (a) data-based convergent synthesis design, where qualitative and quantitative evidence is analyzed together using the same synthesis method, (b) results-based convergent synthesis design, where qualitative and quantitative evidence is analyzed separately using different synthesis methods and results of both syntheses are integrated during a final synthesis, and (c) parallel-results convergent synthesis design consisting of independent syntheses of qualitative and quantitative evidence and an interpretation of the results in the discussion.ConclusionsPerforming systematic reviews of qualitative and quantitative evidence is challenging because of the multiple synthesis options. The findings provide guidance on how to combine qualitative and quantitative evidence. Also, recommendations are made to improve the conducting and reporting of this type of review.
Highlights
Systematic reviews of qualitative and quantitative evidence can provide a rich understanding of complex phenomena
The analysis focused on three concepts inspired by the literature on mixed methods research [22,23,24]: (a) synthesis methods, (b) sequence of data synthesis, and (c) integration of data and synthesis results
We considered there was a sequence because the results of the qualitative synthesis informed the quantitative synthesis. (c) Integration: In the literature on mixed methods research, integration is defined as the process of bringing qualitative and quantitative approaches together and can be achieved at the level of the design, the methods, and the interpretation and reporting [35, 36]
Summary
Systematic reviews of qualitative and quantitative evidence can provide a rich understanding of complex phenomena. While reviews focusing on RCTs can help to answer the question, “What works for whom?,” other important questions remain unanswered such as “Why does it work?,” “How does it work?,” or “What works for whom in what context?.”. Such questions can be addressed by reviewing qualitative evidence. The analysis of qualitative evidence can complement those of quantitative studies by providing better understanding of the impact of contextual factors, helping to focus on outcomes that are important for patients, families, caregivers, and the population and exploring the diversity of effects across studies [4]
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