Evidence synthesis is an approach to research that allow scholars, practitioners and students to find, gather, evaluate, analyse and synthesize existing research on a specific topic or question. It is an umbrella term that encompasses numerous and distinct methods for accomplishing these goals. More than a generic literature review, evidence synthesis methods have various and unique specificities and characteristics. Which method or approach the researcher or research team uses will largely depend on the research question being asked.
For an overview of the main methods used in evidence synthesis, read this landmark paper:
Grant, M. J., & Booth, A. (2009). A typology of reviews: an analysis of 14 review types and associated methodologies. Health Information and Libraries Journal, 26(2), 91–108. https://doi.org/10.1111/j.1471-1842.2009.00848.x
Qualitative evidence synthesis (QES) is a mode of evidence synthesis that poses research questions about existing qualitative studies on a particular topic, theory or phenomenon. Ideally, QES does not simply summarize the results of similar studies, rather quality QES seeks to create new understanding or interpretation of the results of multiple studies, taken as a whole. It extends the findings of these studies as distinct parts and creates an analysis that sheds new light on the subject. Ultimately QES tells a story about the evolution of disciplinary knowledge; it explains how knowledge has developed and changed over time as research is conducted. It will reveal where there has been divergence, controversy, agreement and consensus.
QES is not - strictly speaking - a systematic review. It shares many similar methodological features with a systematic review, but ultimately its goals are different. The searching is done in a systematic way, but due to several limitations inherent to qualitative research indexing, it is difficult to create the replicable and exhaustive searching that is required of a systematic review. Similar to the systematic review, a QES cannot be done alone due to the risk of bias in study selection and appraisal.
Other terms that are used to describe QES include:
• Qualitative systematic review
• Qualitative meta-synthesis
• Qualitative research synthesis
This research guide will walk through the steps of a QES and provide the user with the information they require to make an informed decision about question formulation, protocol creation, methodology, modes for analysis, and frameworks for reporting.
The structure of this guide is based on the most current guidance from authors on the Cochrane Qualitative and Implementation Methods Group:
Flemming, K., & Noyes, J. (2021). Qualitative Evidence Synthesis: Where Are We at? International Journal of Qualitative Methods, 20, 1609406921993276. https://doi.org/10.1177/1609406921993276
as well as Chapter 21: Qualitative Evidence in this key resource:
Noyes J, Booth A, Cargo M, Flemming K, Harden A, Harris J, Garside R, Hannes K, Pantoja T, Thomas J. Chapter 21: Qualitative evidence. In: Higgins JPT, Thomas J, Chandler J, Cumpston M, Li T, Page MJ, Welch VA (editors). Cochrane Handbook for Systematic Reviews of Interventions version 6.4 (updated August 2023). Cochrane, 2023. Available from www.training.cochrane.org/handbook.
Choosing the right research method can be a challenge. Ultimately, the nature of your research question should be the main driver for your decision. If you know that you are not going to take on an original research project, and instead will be focussing on a review/evidence synthesis of some sort, your first stop should be Right Review. This is a tool that will guide you through a series of questions about your research question. It will make a recommendation for the best approach to your project. Even if you don't end up choosing the suggested method, it is a useful exercise and will potentially introduce you to new methods you may want to explore further.
A good rule of thumb, however, is to ask yourself "Am I interested in learning about how people experience a particular phenomenon or intervention?" If the answer is yes - even vaguely so - you should look closer at QES as an approach to your research.
Booth, A., Noyes, J., Flemming, K., Gerhardus, A., Wahlster, P., van der Wilt, G. J., Mozygemba, K., Refolo, P., Sacchini, D., Tummers, M., & Rehfuess, E. (2018). Structured methodology review identified seven (RETREAT) criteria for selecting qualitative evidence synthesis approaches. Journal of Clinical Epidemiology, 99, 41–52. https://doi.org/10.1016/j.jclinepi.2018.03.003