In the data synthesis section, you will present the main findings of your evidence synthesis. As an evidence synthesis summarizes existing research, there are a number of ways in which you can synthesize the results from your included studies.
If the studies you have included in your evidence synthesis are sufficiently similar, i.e., homogenous, you can synthesize the data from these studies using a process called meta-analysis. As the name suggests, a meta-analysis uses a statistical approach to bring together results from multiple studies. For more information about meta-analyses, see Chapter 10 of the Cochrane Handbook for Systematic Reviews of Interventions.
If the studies you have included in your evidence synthesis are not similar (e.g., you have included different research designs due to diversity in the evidence base), then a meta-analysis is not possible. In this instance, you can synthesize the data from these studies using a process called narrative or descriptive synthesis.
A word of caution here – while the process underpinning meta-analysis is well established and standardized, the process underpinning narrative or descriptive synthesis is subjective. There is no one standard process for undertaking this. If you intend to submit your evidence synthesis to a particular journal, it may be worth consulting published evidence syntheses in that journal and/or the journal's editorial guidelines for examples and guidance.
Evidence syntheses of qualitative research have become increasingly popular lately. Data synthesis in these studies may be termed as meta-synthesis. As with narrative or descriptive syntheses, there are a myriad of approaches to meta-synthesis.
(Much of the above content courtesy of University of South Australia Library.)
Regardless of whether an evidence synthesis presents qualitative or quantitative information, reporting out using the PRISMA flow diagram is recommended. The PRISMA website and its many adaptations can be very helpful in understanding components of systematic reviews, meta-analyses, and related evidence synthesis methods. See the Guidelines & Standards tab in this guide for more on PRISMA.