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Systematic reviews, scoping reviews and other evidence syntheses

Overview of evidence synthesis reviews and relevant strategies, tools and resources.

Develop a search strategy

Search strategy

  • refers to the specialized combination of keywords, subject headings, search syntax and logic operators used to retrieve the optimal number of studies for an evidence synthesis project
  • your search strategy should be comprehensive and designed to collect all available relevant evidence on a research question, including peer-reviewed and grey literature

Reporting search strategies

Search strategies are critical components of evidence synthesis research and are:

  • documented and described in the Methods section of published reviews

  • included as an Appendix in published reviews

Expert guidance from librarians

Key evidence synthesis organizations (IOMCochraneCIHRCampbell Collaboration) highlight the importance of librarian expertise in developing search strategies which are:

  • Free from bias as possible
  • Transparent 
  • Reproducible

Building a search strategy

Expect an iterative process, beginning with preliminary searching before developing a final comprehensive search strategy.

  • Preliminary searching:
    • Identify key terms, synonyms and subject headings to use in your search
    • Find existing systematic reviews on any component of your topic and review search strategies included in the methods or appendix
  • Comprehensive searching:
    • Develop a full search strategy including:
      • keywords, synonyms and subject headings
      • appropriate search syntax and logic operators
    • Identify appropriate subject databases for your topic (e.g. MEDLINE, CINAHL)
      • important to search in multiple databases because each database has unique content; evidence syntheses searching must be as comprehensive as possible
    • Run a trial search in one database to test its efficacy; revise search as needed
    • Run searches in other relevant databases

Other sources to search

  • Determine relevant grey literature sources and search with modified strategies
  • Hand search additional relevant non-indexed journals or conference proceedings, if appropriate
  • Contact experts, including corresponding authors of included studies, to find out about additional or ongoing studies

While you are searching

  • Export results from all search processes to a citation manager
  • Keep track of the number of search results retrieved from each database or other information source, e.g. grey literature


Search techniques

You will develop a sophisticated combination of keywords, subject headings, search syntax and logic operators to retrieve the optimal number of studies for an evidence synthesis project

  • Keywords -- natural language words describing the main concepts in your research e.g. if your research question is investigating the effects of social media on adolescents' well-being, your topic keywords are:
    • social media
    • well-being
    • adolescents 
      • Always generate synonyms and related terms for each keyword to ensure you capture studies which investigate the same topic but use different descriptors e.g. adolescent - teenager, young adult, youth, etc.
  • Subject headings -- controlled vocabulary assigned by databases to articles about specific topics; helps broaden your search by ensuring you retrieve relevant studies which may use varying keywords
    • To be comprehensive, use a mix of subject headings and keywords in your search strategy
  • Truncation -- use an asterisk (or other symbol specific to a database) to retrieve alternate word endings; broadens your search. e.g. teen* retrieves teens, teenager, teenagers, teenaged
  • Exact phrase -- enclose 2-3 words or a short phrase in quotes to ensure they are searched together instead of independently e.g. "social media"
  • Logic operators -- connect your search terms to both broaden and focus your search results
    • OR -- broadens search by retrieving ANY of the search terms e.g. teen* OR adolescent OR "young adult"
    • AND -- focuses search by retrieving ALL of the search terms e.g. teen* AND "social media"
    • NOT -- focuses search by removing irrelevant results e.g. "social media" NOT Twitter; use with care to avoid missing studies that include both of your terms
  • Adjacency searching -- use a proximity operator e.g. NEAR, WITHIN to find words which appear within a certain number of words of each other e.g. social N3 media; social W2 media
  • Parentheses -- connect related words e.g. ("social media" OR Twitter OR Facebook) AND (adolescent* OR "young adult*")

Search tutorials and tips

Documentation and tutorials for core and common subject resources

Systematic review database searching cheat sheet - health focus

Subject and niche databases

Limits and filters

Search limits

  • Database search results can often be limited by e.g. year, gender, species, etc.
  • Generally, avoid using these filters as they introduce bias into your search results
  • Search filters are appropriate when:
    • updating an existing search
    • updating an existing systematic review

Search filters

  • Also called hedges, these are pre-designed search strings which allow you to filter your search results e.g. by study design without sacrificing sensitivity/specificity or introducing major sources of bias
  • Always use a critically appraised search filter from one of these organizations: