Should I conduct a meta-analysis?

In the data synthesis section, you need to 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 results from your included studies.

Meta-Analysis for Homogenous Quantitative Data

If the studies you have included in your evidence synthesis are sufficiently similar, or in other words 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. There are many advantages to undertaking a meta-analysis. You may choose to consult with a statistician for advice before proceeding with a meta-analysis. 

Narrative Synthesis for Heterogenous Quantitative Data

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 and there is no one standard process for undertaking this.

Meta-Synthesis for Qualitative Data

In recent times, evidence syntheses of qualitative research is gaining popularity. Data synthesis in these studies may be termed as “meta-synthesis”. As with narrative or descriptive synthesis, there are a myriad of approaches to meta-synthesis.

(the above content courtesy of University of South Australia Library)

Regardless of whether an evidence synthesis presents qualitative or quantitative information, the PRISMA flow diagram provides a structure for reporting results. Many journals follow the PRISMA guidelines, so it is highly recommended for all systematic reviews (and other evidence syntheses). The PRISMA website and its many adaptations can be very helpful in understanding components of systematic reviews, meta-analyses and related evidence synthesis methods 

PRISMA provides a list of items to consider when reporting results. 

• Study selection:  Give numbers of studies screened, assessed for eligibility, & included in the review, with reasons for exclusions at each stage, ideally with a flow diagram.

• Study characteristics:  For each study, present characteristics for which data were extracted (e.g., study size, PICOs, follow-up period) & provide the citations.

• Risk of bias within studies:  Present data on risk of bias of each study &, if available, any outcome level assessment.

• Results of individual studies:  For all outcomes considered (benefits or harms), present, for each study: (a) simple summary data for each intervention group  (b) effect estimates & confidence intervals, ideally with a forest plot. 

• Synthesis of results:  Present results of each meta-analysis done, including confidence intervals & measures of consistency.

• Risk of bias across studies:  Present results of any assessment of risk of bias across studies.

• Additional analysis:  Give results of additional analyses, if done (e.g., sensitivity or subgroup analyses, meta-regression).

PRISMA Tools

• Flow Diagram Generator

  This is an updated version of the original PRISMA flow generator. Includes a downloadable PDF version.

• Flow Diagram (PRISMA)

  Contains both PDF & Word versions. From PRISMA.

Many peer-reviewed research journals publish systematic reviews and other evidence syntheses alongside original/primary research studies. Be sure to read the Author Guidelines for any journal in which you hope to publish. In addition some journals specialize in publishing systematic reviews, such as JBI Evidence Synthesis and Campbell Systematic Reviews.

Your librarian can help you identify journals that publish systematic reviews in your field. 

WMU Libraries strongly encourages researchers to consider publishing in open access formats. Many journals and funding agencies are also requiring researchers to publish their data in open access repositories. Our Data Librarian can assist you with curating, managing, and sharing your data.