Systematic Reviews: Synthesis & Meta-Analysis

Synthesis involves pooling the extracted data from the included studies and summarizing the findings based on the overall strength of the evidence and consistency of observed effects. All reviews should include a qualitative synthesis and may also include a quantitative synthesis (i.e. meta-analysis). Data from sufficiently comparable and reliable studies are weighted and evaluated to determine the cumulative outcome in a meta-analysis.  Tabulation and graphical display of the results (e.g. forest plot showing the mean, range and variance from each study visually aligned) are typically included for most forms of synthesis. Generally, conclusions are drawn about the usefulness of an intervention or the relevant body of literature with suggestions for future research directions.

An AHRQ guide and chapters 9, 10, 11, and 12 of the Cochrane Handbook and further address meta-analyses and other synthesis methods.

Consult Cochrane Interactive Learning Module 6: Analyzing the Data and Module 7. Interpreting the Findings for further information.  *Please note you will need to register for a Cochrane account while initially on the Mayo network. You'll receive an email message containing a link to create a password and activate your account.*

1. Morton SC, Murad MH, O’Connor E, Lee CS, Booth M, Vandermeer BW, Snowden JM, D’Anci KE, Fu R, Gartlehner G, Wang Z, Steele DW. Quantitative Synthesis—An Update. 2018 Feb 23. In: Methods Guide for Effectiveness and Comparative Effectiveness Reviews [Internet]. Rockville (MD): Agency for Healthcare Research and Quality (US); 2008–.

2. McKenzie, JE, et al. Chapter 9: Summarizing study characteristics and preparing for synthesis. In: Higgins JPT, et al. (editors). Cochrane Handbook for Systematic Reviews of Interventions version 6.2. Cochrane, 2021. Available from www.training.cochrane.org/handbook
   See - Section 9 

3. McKenzie, JE, et al. Chapter 9: Summarizing study characteristics and preparing for synthesis. In: Higgins JPT, et al. (editors). Cochrane Handbook for Systematic Reviews of Interventions version 6.2. Cochrane, 2021. Available from www.training.cochrane.org/handbook
   See - Section 9 

4. Deeks, JJ, et al. Chapter 10: Analysing data and undertaking meta-analyses. In: Higgins JPT, et al. (editors). Cochrane Handbook for Systematic Reviews of Interventions version 6.2. Cochrane, 2021. Available from www.training.cochrane.org/handbook
   See - Section 10 

5. Chaimani, A, et al. Chapter 11: Undertaking network meta-analyses. In: Higgins JPT, et al. (editors). Cochrane Handbook for Systematic Reviews of Interventions version 6.2. Cochrane, 2021. Available from www.training.cochrane.org/handbook
   See - Section 11 

6. McKenzie, JE, Brennan SE. Chapter 12: Synthesizing and presenting findings using other methods. In: Higgins JPT, et al. (editors). Cochrane Handbook for Systematic Reviews of Interventions version 6.2. Cochrane, 2021. Available from www.training.cochrane.org/handbook
   See - Section 12 

7. Campbell M, McKenzie JE, Sowden A, et al. Synthesis without meta-analysis (SWiM) in systematic reviews: reporting guideline. BMJ (Clinical research ed). 2020;368:l6890.

8. Alavi M, Hunt GE, Visentin DC, Watson R, Thapa DK, Cleary M. Seeing the forest for the trees: How to interpret a meta-analysis forest plot. Journal of advanced nursing. 2021;77(3):1097-1101. doi:https://dx.doi.org/10.1111/jan.14721