How do we take a large body of evidence and turn it into useful information? There are a few ways to do this.
In the past, we relied primarily on narrative reviews.
In a narrative review, a subject matter expert addresses a research question by surveying and summarizing some of the existing literature. The expert then interprets that literature based on his or her personal experience. These reviews can be useful, but are limited. First, the research included is based only on the expert’s knowledge, not a full review of the existing literature. Second, a narrative review is inherently biased because it’s based on the opinions of one expert.
An alternative to this approach is a systematic review.
A systematic review seeks to systematically and search for, evaluate, and synthesize existing research. It includes a qualitative and perhaps quantitative analysis of what is known and unknown, as well as recommendations for action and future research.
Depending on the evidence you’re synthesizing, your systematic review might also include meta-analysis.
Meta-analysis uses statistics to combine information from different studies to produce a quantitative summary of their findings.