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Systematic Reviews: The Process: Searching

Developing the Search


IOM Standard 3.1; Conduct a comprehensive systematic search for evidence

3.1.1  Work with a librarian or other information specialist trained in performing systematic reviews to plan the search strategy

3.1.2  Design the search strategy to address each key research question

3.1.3  Use an independent librarian or other information specialist to peer review the search strategy

3.1.4  Search bibliographic databases

3.1.5  Search citation indexes

3.1.6  Search literature cited by eligible studies

3.1.7  Update the search at intervals appropriate to the pace of generation of new information for the research question being addressed

3.1.8  Search subject-specific databases if other databases are unlikely to provide all relevant evidence

3.1.9  Search regional bibliographic databases if other databases are unlikely to provide all relevant evidence

STANDARD 3.2  Take action to address potentially biased reporting of research results

3.2.1  Search grey literature databases, clinical trial registries, and other sources of unpublished information about studies

3.2.2  Invite researchers to clarify information about study eligibility, study characteristics, and risk of bias

3.2.3  Invite all study sponsors and researchers to submit unpublished data, including unreported outcomes, for possible inclusion in the systematic review

3.2.4  Handsearch selected journals and conference abstracts

3.2.5  Conduct a web search

3.2.6  Search for studies reported in languages other than English if appropriate

Search Strategy

Searches for systematic reviews aim to be as extensive as possible in order to ensure that as many as possible of the necessary and relevant studies are included in the review. It is, however, necessary to strike a balance between striving for comprehensiveness and maintaining relevance when developing a search strategy. Increasing the comprehensiveness (or sensitivity) of a search will reduce its precision and will retrieve more non-relevant articles

The goal is to maximize recall and precision while keeping the results manageable. Recall (sensitivity) is defined as the number of relevant reports identified divided by the total number of relevant reports in existence. Precision (specificity) is defined as the number of relevant reports identified divided by the total number of reports identified.  Issues to consider:

  • All concepts are included in the strategy
  • All appropriate subject headings are used
  • Appropriate use of explosion
  • Appropriate use of subheadings and floating subheadings
  • Use of natural language (text words) in addition to controlled vocabulary terms
  • Use of appropriate synonyms, acronyms, etc.
  • Truncation and spelling variation as appropriate
  • Appropriate use of limits such as language, years, etc.
  • Field searching, publication type, author, etc.
  • Boolean operators used appropriately
  • Line errors—when searches are combined using line numbers, be sure the numbers refer to the searches intended
  • Check indexing of relevant articles
  • Search strategy adapted as needed for multiple databases

TIP:  Look for systematic reviews already published.  This serves 2 purposes:

     1. Makes sure that the work has not already been done

     2. Provides examples of search strategies for your topic

Searching Manuals and Checklists