This guide is a work-in-progress!
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Evidence synthesis interprets individual studies within the broader context of existing knowledge, providing a rigorous foundation for informed decision-making in policy and clinical practice. It uses transparent methodologies to systematically (orderly) address questions through study selection, appraisal, analysis, and evidence strength assessment. This comprehensive approach ensures that research is understood in context, which is essential for effective decision-making, especially when studies may conflict. Evidence synthesis methods are applied across diverse fields, including education, health care, and environmental conservation, and are utilized by various organizations.
Adapted from: https://evidencesynthesis.org/what-is-evidence-synthesis/
It's important to understand the differences between a traditional literature review and evidence synthesis. Review the table below for some comparisons.
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Literature Review |
Evidence Synthesis |
|
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. |
|
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Attempts are made to find all existing published and unpublished literature on the research question.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
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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
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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
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Conclusions are more qualitative and may not be based on study quality. |
Bases conclusions on quality of the studies and provide recommendations for practice or to address knowledge gaps. |
Adapted from https://guides.library.cornell.edu/evidence-synthesis/intro
1. Systematic vs. Scoping Review
2. Which review is right for you?
4. Systematic Review Decision Tree
5. A typology of reviews: an analysis of 14 review types and associated methodologies (article)
A systematic review seeks to systematically search for, appraise, and synthesis research evidence. It adheres to guidelines on the conduct of a review.
It aims for exhaustive and comprehensive searching, and the quality assessment may determine inclusion and exclusion.
The synthesis is usually narrative with accompanying tables. It's analysis provides information on what is know and recommendations for practice. It also shows what's unknown, uncertainty about findings, and recommendations for future research.
A scoping review is a preliminary assessment of potential size and scope of available research literature. This review aims to identify extent and qualities of research evidence, including ongoing research.
The completeness of the search is determined by whatever time/scope restraints exist. It can include research in progress. There is no formal quality assessment.
The synthesis is usually tabular (using tables to display information) with some narrative. The analysis characterizes the quality and quantity of literature, maybe by study design or other key features. It attempts to specify a applicable review.
A rapid review is the assessment of what's already known about an issue by using systematic review methods for searching and appraising existing research.
The completeness of the search is determined by whatever time restraints exist. There is a time-limited formal quality assessment.
The synthesis is usually narrative and tabular, and there is an analysis of quantities of literature and overall direction of effect of literature.
A literature review is a work which examines recent or current literature in a field. It can cover subjects of a wide range at various levels of comprehensiveness. A lit review can include research findings at times.
It may or may not include comprehensive searching or quality assessment.
It is usually narrative and the analysis may be chronological, conceptual, thematic, among others.
A meta-analysis statistically combines results of qualitative studies to provide more precise effects of the results.
It aims for comprehensive searching and could use funnel plot (or scatter plot) to assess completeness. The quality assessment may determine inclusion/exclusion and/or sensitivity analyses.
The synthesis is graphical and arranged in a table (with rows and columns). The analysis is numerical of measures of effect, assuming absence of diversity.
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