Evidence and Gap Maps

What are Evidence and gap maps (EGM)?  

EGMs are systematic presentations of all available evidence for a particular sector or sub-sector. A typical map is a matrix of intervention categories (rows) and outcome domain (columns). There may be additional filters for study design, location and population sub-group.

EGMs show what evidence there is and not what evidence says!

Evidence and gap maps must:

  • Have a pre-specified protocol
  • Have a systematic search strategy
  • Have clear inclusion and exclusion criteria which are systematically applied
  • Systematically report all eligible studies

Evidence may be global or for a particular region(s). It may cover different types of evidence (but most examples are of effectiveness studies), and may include primary studies and systematic reviews.

 Why make evidence and gap maps? Because they:

  • Guide users to available high quality evidence to inform strategy and programme development
  • Tell users where there is no high quality evidence
  • Identify gaps to be filled by evidence synthesis and new studies for researchers and research commissioners – and so more strategic, policy-oriented approach to research agenda

If you would like to know more in order to make one, read more here.

Comparison of EGMs and systematic reviews


Systematic review

Evidence and gap map


Question setting Often restricted to a single intervention, and a limited range of outcomes. A PICOS is specified to guide study inclusion criteria.  Broad scope of interventions across a sector or sub-sector, with full range of outcomes across causal chain. A PICOS is specified to guide study inclusion criteria.  EGMs are broader in scope than systematic reviews.
Search  strategy A comprehensive and systematic search for primary studies meeting the inclusion criteria (and not exclusion criteria) A comprehensive and systematic search for systematic reviews and primary studies meeting the inclusion criteria (and not exclusion criteria) No difference in approach. EGMs search for systematic reviews as well as primary studies.
Screening Identified studies screened against inclusion and exclusion criteria Identified studies screened against inclusion and exclusion criteria No difference in approach
Coding and data extraction Coding of study and intervention characteristics, moderators and data extraction of effect sized and related statistics Coding of a limited number of study and intervention characteristics EGMs require coding of less data than systematic reviews
Critical appraisal Assessment of quality of included studies using a critical appraisal instrument Critical appraisal may not be done, but is recommended Critical appraisal is optional for EGMs
Evidence synthesis Statistical or narrative synthesis of the evidence Not done EGMs do not synthesize the evidence
Reporting Systematic reporting of evidence Graphical representation of map availability of evidence. Descriptive overview of map. Systematic reviews summarize what the evidence says. EGMs only summarize what evidence is available.
Use To inform policy and practice To inform research priorities and research funding Systematic reviews are to inform policy, and EGMS primarily to inform research priorities.


 There are lots of evidence maps and they don’t all look the same. 

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