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Data Synthesis

What It Is | PRISMA Flow Diagram | Narrative Synthesis | Tables | Manuals & Guidance

What It Is

After you have collected your data, the next step is data synthesis. According to the Cochrane Handbook for Systematic Reviews of Interventions, “Synthesis is a process of bringing together data from a set of included studies with the aim of drawing conclusions about a body of evidence” (Cochrane).

You will present your evidence synthesis review results in various ways: narrative or descriptive syntheses and tables and/or figures for scoping and systematic reviews, and possibly a meta-analysis for systematic reviews.  

Combining statistics from your included studies is a meta-analysis. A meta-analysis is possible if the included studies from your systematic review are homogenous (i.e., alike). See Chapter 10: Analysing data and undertaking meta-analyses in the Cochrane Handbook for more details.  Similarly, if you are using qualitative data, you may do a meta-synthesis.  

PRISMA Flow Diagram

No matter the type of review conducted, a PRISMA Flow Diagram is required. Use the template provided by PRISMA and an appropriate extension for your evidence synthesis type.

If you worked with an NIH Librarian on your evidence synthesis, they can assist with creating the PRISMA Flow Diagram. If you have any questions on this step, contact the NIH Library.

Below is an example of an empty PRISMA Flow Diagram that each review team would complete. You can download the template in PDF or Microsoft Word format and should customize it with your review's results. Obtain the numbers to put into the boxes from the software used to screen and from the librarian that conducted the searches.

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PRISMA Flow Diagram shows the flow of information from the start to the end of the process. It includes the total numbers of articles retrieved, number of duplicates identified and numbers included and excluded after each stage of screening.

Narrative or Descriptive Synthesis

In a narrative synthesis:

  • Text and tables summarize and explain your findings
  • Describe study characteristics, context, and findings for each individual included study and all the included studies as a group
  • Different thematic analysis approaches may be used for synthesizing the study findings for individual included studies and all the included studies as a group

For example, for individual included studies, provide details on participants, setting, exposure/intervention, outcomes, and other factors relevant to your research question (e.g., age, sex/gender, race or ethnicity of participants, length of exposure/intervention, sample size, etc.).

For describing as a group all your included studies, you might sub-group studies based on relevant criteria and summarize that sub-group’s key aspects.

Additionally, quantitative and qualitative data are synthesized differently regardless of the type of review conducted. For more information on synthesizing qualitative data, see articles by Higgins etal. 2019 and Noyes etal. 2019, and chapters from the Cochrane Handbook and JBI Manual for Evidence Synthesis for more information.

Tables

Here your data may be presented in a table format to summarize all your included studies (e.g., key characteristics table), and for a systematic review also include an evidence summary table. It is helpful to present key characteristics related to each included study (e.g., population, intervention/exposure, outcomes, setting, and other key features) in a table to help you and eventually your reader understand your results.

For examples of key characteristics or evidence summary tables, ask a NIH Librarian for additional help.

Manuals & Guidance

To learn more about synthesizing the data for your review, please refer to the resources listed below which contain much more detail and information on this important step. You can ask a NIH Librarian for additional help.

Evidence Synthesis > Select, Collect & Synthesize

Eligibility Criteria | Screening | Using Covidence | Risk of Bias | Data Collection | Data Synthesis