University of Canberra
Skip to Main Content

Systematic Reviews in Health

Synthesizing the Evidence

Narrative Synthesis

Once the extraction and appraisal of individual included studies is completed, a narrative synthesis is required.  The purpose of the synthesis is to bring together the principal findings of the Systematic Review in a narrative (i.e. text) form.  Reviewers should also consider including a "Summary of Findings" table to support the narrative in a clear format.

Text and tables provide an initial descriptive summary and explanation of the characteristics and findings of the included studies. However, simply describing the studies is not sufficient for a synthesis.  The narrative synthesis must provide an analysis of the relationships within and between studies to provide an overall assessment of the robustness of the evidence.1

Strength of Evidence

The synthesis should comment on the strength of the evidence for each main finding/outcome.  Reviewers may consider applying the GRADE system for evaluating the strength of the evidence for each finding/outcome.


A meta-analysis is a statistical analysis of the data (numbers) from the individual studies.  Meta-analyses are usually performed with a specialised software package and require an examination of funnel and forest plots.  Depending on where a Systematic Review will be published, a corresponding software package may need to be used - For example RevMan for Cochrane Reviews.  

By nature, narrative synthesis is a more subjective process than meta-analysis and therefore, the approach used should be rigorous and transparent to reduce the potential for bias.

Introducing GRADE for Summarizing the Quality of Evidence

Grading of Recommendations Assessment, Development, and Evaluation (GRADE) offers a transparent and structured process for developing and presenting summaries of evidence, including its quality, for Systematic Reviews and recommendations in health care.

GRADE process

In GRADE, randomised controlled trials (RCTs) start as high-quality evidence and observational studies as low-quality evidence supporting estimates of intervention effects.  Various factors may lead to rating down or up the quality of evidence until ultimately, the quality of evidence for each outcome falls into one of four categories from high to very low.2

GRADE factors


1. O'Connor, E., Whitlock, E., & Spring, B. (2007). Introduction to systematic reviews. Available:

2. Guyatt, G., et al. (2011). "GRADE guidelines: 1. Introduction—GRADE evidence profiles and summary of findings tables." Journal of Clinical Epidemiology 64, 4, 383-394. Available: doi:10.1016/j.jclinepi.2010.04.026