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Evidence Synthesis and Systematic Reviews

This guide will help you get started with your next evidence synthesis review

Diagnostic Test Accuracy Review

Definition: "Systematic reviews of diagnostic test accuracy provide a summary of test performance based on all available evidence, evaluate the quality of published studies, and account for variation in findings between studies." JBI Reviewers Handbook

When to use: When assessing the evidence from diagnostic test accuracy studies

Limitations: The unfamiliarity of methods and accuracy metrics makes it difficult to convey results to a wide audience. Results can be misinterpreted.


Integrative Reviews

Definition: "A review method that summarizes past empirical or theoretical literature to provide a more comprehensive understanding of a particular phenomenon or healthcare problem (Broome 1993). Integrative reviews, thus, have the potential to build nursing science, informing research, practice, and policy initiatives. Well-done integrative reviews present the state of the science, contribute to theory development, and have direct applicability to practice and policy." 

When to use: To review experimental and non-experimental research simultaneously, to define concepts, to review theories, to review evidence/point out gaps in the literature, to analyze methodological issues.  Good for nursing issues.

Limitations: The combination and complexity of incorporating diverse methodologies can contribute to lack of rigor, inaccuracy, and bias, methods of analysis, synthesis, and conclusion-drawing remain poorly formulated, issues related to combining empirical and theoretical reports.


Living Systematic Reviews

Definition: A systematic review which is continually updated, incorporating relevant new evidence as it becomes available by continual, active monitoring of the evidence.  They immediately include any new important evidence identified and are supported by up-to-date communication about the status of the review.

When to use: When there is a high priority (or emerging) question for policy and practice, important uncertainty in the existing evidence, emerging evidence that is likely to impact on what is currently known.

Limitations: Time consuming with continuous work flows, frequent searching and screening, team members must have a long term commitment to the project, frequent statistical analysis-can lead to inflated false-positive rate, may require technological tools to support screening, data extraction and critical analysis or risk of bias assessment, no clear agreement on methods to manage data synthesis


Mapping Reviews

Definition: Mapping reviews are focused on a visual synthesis of the data and are question based rather than topic based like the scoping review.

When to use: When there is an abundance and a diversity of research, as a first step to a systematic review, or to identify gaps in a topic area.

Limitations: The broad nature and rapid search may mean that some articles will be missed. They may require additional expertise or training for creating the visual output. "Foundational work is needed to better standardize the methods and products of an evidence map..." (Miake et. al. 2016)


Meta-ethnography (also known as meta-synthesis)

Meta-ethnography (also known as meta-synthesis)

Definition: A meta-ethnography brings together qualitative data to form a new interpretation of the research field.  It helps to build new theories and is not to be confused with a meta-analysis which tests a hypothesis using quantitative data.  It primarily generates theory such as program theory, implementation theory, or an explanatory theory of why the intervention works or not; hypothesis for future testing or comparison with trial outcomes.

When to use: Meta-ethnography are best designed to re-interpret meaning across many qualitative studies which could be across subject areas.

Limitations: Only appropriate for high-quality qualitative studies, can only accommodate a limited number of primary studies, choice of a meta-ethnography may not be confirmed until pool of evidence known, requires significant methodological skill and experience with qualitative methods, may take time to engage with the evidence and develop theory.


Mixed Methods Reviews

Definition:  Synthesizes qualitative and quantitative evidence to provide a more inclusive answer to informs clinical policy or organizational decisions. 

When to use: For multidisciplinary topics or topics with a body of literature that includes quantitative, qualitative, and mixed methods studies, to determine not only the effects of interventions but also their appropriateness, to identify research gaps, to provide an explanation for possible heterogeneity between trials, to answer multiple questions in one systematic review.

Limitations: They require significant methodological skill, they are resource intensive because they may take time to engage with the evidence and develop theory. They are not inherently reproducible or transparent because of the highly iterative nature of the interpretative process


Network Meta Analysis

Definition: "Network meta-analysis compares multiple interventions simultaneously by analyzing studies making different comparisons in the same analysis." Source: M. Petticrew et al. (2013)

When to use: For conditions with multiple interventions, where there are many combinations of direct or indirect interactions, to make treatment estimates for an entire treatment network instead of scanning each individual pair-wise comparison, to give the "full picture" to clinicians, potential to more explicitly "rank" treatments using summary outputs

Limitations: Requires specialist statistical expertise and software, assumes that all interventions included in the "network" are equally applicable to all populations and contexts of the studies included.


Overview of Reviews (Umbrella Review)

Definition: A systematic review of systematic reviews.  Examines two or more systematic reviews or evidence syntheses. "The intent of this kind of review is to include systematic reviews or meta-analyses as the main study type and thus examine only the highest level of evidence."  Blackwood D (2016)

When to use: When synthesizing and combining relevant data from existing systematic reviews or meta-analyses to make better decisions, to provide clinical decision makers with the evidence they need when there are many systematic reviews.

Limitations: Limited evidence sources.  It is impossible to do an umbrella review without a core of systematic reviews on the topic.


Review of Complex Interventions

Definition: reviews of interventions that have multiple components and complicated/multiple causal pathways, feedback loops, synergies, and/or mediators and moderators of effect.  They may also have additional complexity through population, implementation and/or context.

When to use: When the intervention has multiple components and any component may have an interventional effect, including the specific component of the intervention, between the intervention and study participants, with the intervention context, or a combination of these aspects. 

Limitations: Difficulty knowing whether an intervention is simple or complex, may be more time consuming than a non-complex review as inputs from stakeholders and the use of theory may be necessary, may require substantial adaptation of conventional review methods.