Meta-analysis is a quantitative synthesis method that statistically combines results from comparable studies to estimate an overall effect size, and is primarily. Meta-analysis is preferred for homogeneous, quantitative data.  Meta-analysis is often conducted as part of systematic reviews.  Although the method is qualitative, narrative synthesis should also be included to synthesize findings.

Key steps include:

• Assessing study compatibility: Ensuring studies are sufficiently similar in design and outcomes.
• Calculating effect sizes: Using models (e.g., fixed-effect or random-effects) to pool data.
• Evaluating heterogeneity: Using statistics like I² to assess variability across studies.

Learn More:

Deeks JJ, Higgins JPT, Altman DG (editors). Chapter 10: Analysing data and undertaking meta-analyses. 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. 

Narrative synthesis is a qualitative approach used when statistical pooling is not feasible, often due to heterogeneity in study designs, populations, interventions, or outcomes. Narrative synthesis often uses descriptions, thematic analysis, and tabulation to synthesize findings.  This is ideal for diverse and/or qualitative data.  

• Develop a preliminary synthesis: Organize findings and identify patterns.
• Exploring relationships: Examine how study characteristics influence outcomes.
• Assessing robustness: Consider the strength and consistency of the evidence.

Learn more:

Campbell, M., McKenzie, J. E., Sowden, A., Katikireddi, S. V., Brennan, S. E., Ellis, S., Hartmann-Boyce, J., Ryan, R., Shepperd, S., Thomas, J., Welch, V., & Thomson, H. (2020). Synthesis without meta-analysis (SWiM) in systematic reviews: reporting guideline. BMJ (Clinical research ed.), 368, l6890. https://doi.org/10.1136/bmj.l6890

Cochrane Training. Synthesis Without Meta-analysis (SWiM) reporting guidline. (2020). Cochrane 

Popay, J., Roberts, H., Sowden, A., Petticrew, M., Arai, L., Rodgers, M., Britten, N., Roen, K., & Duffy, S. (2006). Guidance on the conduct of narrative synthesis in systematic reviews. A product from the ESRC methods programme Version, 1(1), b92.