01 · The Question
How Do You Systematically Synthesize Evidence That Is Not Primarily Numerical?
Suppose several qualitative studies have interviewed students about online learning. One examines isolation, another explores flexibility, another investigates relationships with instructors, and others study engagement, accessibility, belonging, or workload.
You could summarize each study separately. But what if you want to understand what these studies collectively reveal about students' experiences across contexts?
That is the territory of qualitative evidence synthesis, commonly abbreviated as QES.
Rather than pooling numerical effect estimates, qualitative evidence synthesis systematically identifies, appraises, and interprets qualitative evidence to develop findings about meanings, experiences, perspectives, processes, contexts, and other phenomena that quantitative effect estimates may not capture.
03 · What You Need to Know
What Qualitative Evidence Synthesis Actually Does
QES Is a Family of Systematic Review Methodologies
Cochrane uses qualitative evidence synthesis as an umbrella term for methodologies associated with the systematic review of qualitative research evidence. A QES may be conducted as a standalone review or form part of a broader review of complex interventions, systems, or guideline development.
You may encounter related labels such as qualitative systematic review, qualitative research synthesis, qualitative synthesis, and meta-synthesis. Terminology varies across methodological traditions. Cochrane specifically prefers qualitative evidence synthesis as the broader term because multiple distinct synthesis methodologies exist within this family.
This distinction matters because saying "we conducted a qualitative synthesis" does not yet tell readers how the synthesis was performed.
QES Answers Questions That Effect Estimates Cannot Answer Well
A quantitative systematic review might ask whether an intervention improves an outcome and by how much. A qualitative evidence synthesis can ask how people experience that intervention, why they accept or reject it, how implementation varies across settings, what barriers and facilitators matter, or how contextual conditions shape its use.
Cochrane identifies several contributions of qualitative evidence, including understanding people's experiences and attitudes, explaining intervention complexity, examining implementation, and identifying how individual and contextual characteristics influence effects.
This makes qualitative synthesis particularly useful when knowing whether something works is insufficient for deciding how, why, for whom, or under what circumstances it might work in practice.
Quantitative evidence synthesis
Often examines numerical quantities such as intervention effects, associations, prevalence, or diagnostic accuracy.
Qualitative evidence synthesis
Examines meanings, experiences, perspectives, processes, contextual influences, implementation, and other interpretive questions using qualitative evidence.
Qualitative Evidence Is More Than Quotations From Participants
Primary qualitative studies contain several levels of information. Participants may provide direct accounts of their experiences. Primary researchers analyze those accounts and develop themes, concepts, interpretations, or explanatory findings. Review authors then work with the reported qualitative evidence to develop a synthesis across studies.
This means QES is not simply a process of collecting interesting quotations from published papers. The unit of synthesis may involve primary-study findings, themes, concepts, interpretations, supporting illustrations, or other forms of qualitative evidence depending on the chosen methodology.
Cochrane also recognizes that qualitative evidence may sometimes be available from qualitative components of mixed-methods studies or relevant narrative data from other sources. Eligibility should follow the review question and methodology rather than a simplistic rule based on the article's label.
Different QES Methods Produce Different Kinds of Knowledge
There is no universally best qualitative synthesis method because different methods pursue different analytic goals.
| Approach |
General Orientation |
Potential Use |
| Thematic synthesis |
Identifies and develops themes across qualitative findings |
Useful for developing descriptive and potentially more analytical themes across studies |
| Framework synthesis |
Uses an existing framework to organize and analyze evidence while allowing refinement where appropriate |
Useful when an established framework or decision structure provides a meaningful starting point |
| Meta-ethnography |
Interpretive approach that examines and translates concepts across studies |
Useful for developing deeper conceptual or theoretical understanding |
| Meta-aggregation |
Aggregates findings into categories and synthesized findings with an emphasis on actionable evidence |
Commonly associated with JBI qualitative evidence synthesis and evidence-informed practice |
These descriptions are necessarily simplified. Each approach has its own methodological assumptions and procedures. Researchers should consult guidance specific to the chosen method rather than treating the methods as interchangeable techniques available from a drop-down menu.
Your Question Should Help Determine the Synthesis Method
Cochrane recommends considering the type and conceptual richness of available qualitative evidence before selecting the synthesis methodology. Some methods are more suitable for producing descriptive findings that can inform action, while others have greater capacity for developing new conceptual or theoretical interpretations.
This means you may need preliminary scoping to understand the evidence base before finalizing every detail of the synthesis method. Cochrane notes that flexible options concerning the choice of method may sometimes need to be articulated prospectively in the protocol.
The method should nevertheless be selected for methodological reasons, not because a particular software package or familiar coding procedure happens to be available.
Searching for Qualitative Evidence Has Its Own Challenges
Qualitative studies can be more difficult to identify consistently than some quantitative study designs. Titles and abstracts may not clearly identify a study as qualitative, terminology varies substantially, and qualitative components may be published separately from associated trials or mixed-methods projects.
Search strategies therefore need to reflect the review question and the characteristics of qualitative evidence. Reviewers may need supplementary approaches to identify related reports or relevant studies that conventional database searches do not retrieve easily.
Unlike some quantitative reviews that seek every eligible study for statistical estimation, certain QES methodologies may also use purposive sampling of eligible qualitative studies when the evidence base is very large. Cochrane notes that study selection for synthesis can depend on conceptual richness, context, and the needs of the synthesis. Such sampling decisions should be methodologically justified and transparently reported.
Critical Appraisal Still Matters
Qualitative research does not become exempt from methodological appraisal because it does not estimate a numerical effect. Reviewers need to examine methodological strengths and limitations of included qualitative studies using criteria appropriate to qualitative research.
JBI, for example, provides a critical appraisal checklist specifically for qualitative research as part of its evidence-synthesis methodology. Cochrane likewise includes assessment of methodological strengths and limitations as a stage in qualitative evidence synthesis.
The purpose is not to force qualitative studies into criteria designed for randomized trials. Appraisal should correspond to the epistemological and methodological characteristics of the evidence being evaluated.
QES Can Stand Alone or Be Integrated With an Effectiveness Review
Qualitative evidence synthesis can be a complete research project in its own right. It can also be linked with a quantitative review.
Suppose an effectiveness review finds that an intervention improves outcomes on average. A linked QES might reveal that participants find the intervention burdensome, that implementation depends heavily on staff training, or that acceptability differs across settings. Those findings can help explain how the intervention operates in practice and why quantitative effects may vary.
Cochrane describes designs in which qualitative evidence synthesis is conducted alongside and subsequently integrated with an intervention review, as well as mixed-method designs in which qualitative and quantitative components are integrated within a single protocol.
Confidence in Synthesized Qualitative Findings Can Be Assessed
Researchers sometimes assume that qualitative synthesis cannot support any structured assessment of confidence. That is incorrect.
GRADE-CERQual provides an approach for assessing how much confidence to place in individual findings from qualitative evidence syntheses. The assessment considers methodological limitations, coherence, adequacy of data, and relevance.
This is conceptually different from calculating a confidence interval around an effect estimate. The purpose is to evaluate confidence in a qualitative review finding, not to convert qualitative interpretation into a probability or numerical effect.
QES Is Not Meta-Analysis With Words
Meta-analysis statistically combines numerical estimates. Qualitative synthesis interprets meaning across qualitative evidence. The underlying data, analytic logic, and epistemological assumptions are different.
Even the term meta-synthesis can create confusion because it sounds like a qualitative counterpart to meta-analysis. In practice, meta-synthesis is used in several ways within qualitative research. The relationship between the terms is explored separately in meta-synthesis versus meta-analysis.
Watch Out
Do not convert qualitative findings into simple frequencies such as "12 of 15 studies mentioned this theme" and assume that the most frequently reported theme is therefore the most important. Frequency can sometimes provide useful descriptive information, but qualitative synthesis concerns meaning, context, richness, and relationships among findings, not merely how often a code appears.
07 · A Quick Checklist
Before Starting a Qualitative Evidence Synthesis
Before conducting the QES, check:
Define a review question that genuinely requires qualitative evidence about experiences, perspectives, meanings, context, processes, or related phenomena.
Conduct preliminary scoping where necessary to understand the type and conceptual richness of the available qualitative evidence.
Choose a qualitative synthesis methodology that matches the review question and intended type of finding.
Develop explicit eligibility and search methods suitable for identifying relevant qualitative evidence.
Use an appraisal approach appropriate to qualitative research and the synthesis methodology.
Define what will be extracted from primary studies and distinguish participant accounts from primary-author interpretations where the methodology requires it.
Document any sampling of eligible qualitative studies and justify why the selected evidence is appropriate for the synthesis.
Consider an appropriate approach such as GRADE-CERQual when confidence in synthesized qualitative findings needs to be assessed.
