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PPIRS Evidence Synthesis Guide

What do we mean by evidence synthesis?

"...a way of combining information from multiple studies that have investigated the same thing, to come to an overall understanding of what they found"
(From the Cochrane website)

The most well-established evidence synthesis methods are meta-analyses and systematic reviews

Why evidence synthesis?

  • Provide guidance for practice and policy-making
  • Identify areas of knowledge gaps and knowledge saturation
  • Decrease bias 
  • Increase reproducibility and transparency

What is a systematic review?

“…a scientific investigation that focuses on a specific question and uses explicit, pre-specified scientific methods to identify, select, assess, and summarize the findings of similar but separate studies.”
(Source: “Finding What Works in Health Care”, Institute of Medicine)

Types of systematic review questions

  • The effectiveness of a treatment or intervention
  • The rate, prevalence or trends of occurrence of a condition
  • The correlation or association of factors
  • The accuracy of a diagnostic test
  • The reliability or validity of a method or measure

Systematic review vs. traditional lit review

Review Stage Traditional Review Systematic Review
Review question Question is broad and terms are not well-defined  Question is specific; terms and protocol are defined in advance
Study selection Convenience sampling and biased selection Exhaustive searches with pre-defined criteria applied for selection by more than one reviewer
Quality assessment None Selected studies assessed for risk of bias and study quality
Synthesis Qualitative and narrative; vote-counting may be used Sometimes quantitative, including meta-analysis with risk of bias considered

Systematic reviews, scoping reviews, systematic maps and rapid reviews

  • Systematic reviews—answer specific questions and include a quality assessment
  • Scoping reviews and systematic maps—questions are often much broader in nature with differences in presentation and use
  • Rapid reviews—an attempt to perform a systematic review in a shorter time period when quick answers are required

Key features and best practices in evidence synthesis

  • At least 2 reviewers
  • Protocols
  • Register research question
  • Document search strategies - your discovery system won’t cut it
  • Common tools

The librarian’s role

Tools & Resources