Guide To Evidence Synthesis
What is Evidence Synthesis?
According to the Royal Society, 'evidence synthesis' refers to the process of bringing together information from a range of sources and disciplines to inform debates and decisions on specific issues. Evidence synthesis generally includes a methodical and comprehensive literature synthesis focused on a well-formulated research question. The aim is to identify and synthesize all of the scholarly research on a particular topic, including both published and unpublished studies. Evidence syntheses are conducted in an unbiased, reproducible way to provide evidence for practice and policy-making, as well as to identify gaps in the research. Evidence syntheses may also include a meta-analysis, a more quantitative process of synthesizing and visualizing data retrieved from various studies.
Evidence syntheses are much more time-intensive than traditional literature reviews and require a multi-person research team. Before embarking on an evidence synthesis project, it's important to clearly identify the purpose. For a list of types of evidence synthesis projects, see Types of Evidence Synthesis.
How does a Systematic Review Differ from a Traditional Literature Review?
One commonly used form of evidence synthesis is a systematic review. This table compares a traditional literature review with a systematic review.
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Traditional Literature Review |
Systematic Review |
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Review Question/Topic |
Topics may be broad in scope; the goal of the review may be to place one's own research within the existing body of knowledge, or to gather information that supports a particular viewpoint. |
Starts with a well-defined research question to be answered by the review. Reviews are conducted with the aim of finding all existing evidence in an unbiased, transparent, and reproducible way. |
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Searching for Studies |
Searches may be ad hoc and based on what the author is already familiar with. Searches are not exhaustive or fully comprehensive. |
Attempts are made to find all existing published and unpublished literature on the research question. The process is well-documented and reported. |
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Study Selection |
Often lack clear reasons for why studies were included or excluded from the review. |
Reasons for including or excluding studies are explicit and informed by the research question. |
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Assessing the Quality of Included Studies |
Often do not consider study quality or potential biases in study design. |
Systematically assesses risk of bias of individual studies and overall quality of the evidence, including sources of heterogeneity between study results. |
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Synthesis of Existing Research |
Conclusions are more qualitative and may not be based on study quality. |
Bases conclusion on quality of the studies and provide recommendations for practice or to address knowledge gaps. |