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Systematic Reviews: Search filters and hedges

Overview of systematic review methodology and key strategies for searching and reporting to the Cochrane Collaboration's Gold Standard

Heading: Search filters and hedges

Search filters and hedges overview

Search hedges are pre-made search strategies which can be incorporated into your search, saving you time.


  • may be methodological or topic-based.
  • can also be referred to as clinical queries, optimal search strategies or filters.
    (however these are NOT the same as the filters you will see in databases)
  • may be formally 'validated' to meet a minimum level of article retrieval sensitivity and precision.

Watch this video from Yale University for an introduction to pre-made search strategies and suggestions of where to find validated hedges.

Video Length: 10:57

  • Building systematic search strategies is complex and time consuming.
  • It can be worth searching for pre-made search strategies that match your concepts.
  • Pre-made search strategies are known as 'filters' or 'hedges'.
  • They may also be called 'optimal search strategies', 'quality filters', or 'clinical queries'.
  • Topic hedges are designed to find resources relevant to a specific topic.
  • Methodological hedges are designed to find specific study design types.
  • These can save time, but there are things to consider before deciding to use existing hedges.
  • Some hedges are expert informed, using scientific validation techniques.
  • Validated sets have been examined to determine their sensitivity and specificity.
  • If a hedge has a sensitivity of 99%, it will retrieve 99% of all articles known to be relevant in a gold standard test set.
  • A hedge with high sensitivity will be very comprehensive, but will require you to filter out some irrelevant results.
  • If a hedge has a specificity of 99%, it filters out 99% of articles that are known to be irrelevant in the gold standard test set.
  • A hedge with high specificity will be extremely focused, but may miss some relevant results.
  • In most cases, you will end up choosing a hedge that has a balance of sensitivity and specificity.
  • Not all hedges are validated - this doesn't mean they are poor quality, but you will have to carefully evaluate the hedge yourself.
  • If a hedge has been validated, consider:
    • the sensitivity and specificity score
    • the database used for validation
    • if you will need to remap the hedge to a new database
    • the subject area of the gold standard test set
    • the date of the validation
  • For details about where to search for hedges, please continue reading the information on this page.

More information

How do I choose one?

Consider whether the search hedge is:

  • current? Subject headings do change over time.
  • relevant to your PICO / PICO element?
  • comprehensive and transparent?
  • validated? What methods were used to develop it?
  • created by an expert Information Manager / Librarian or research group?
  • cited? (Search hedges should be cited when used. If a hedge has not been cited many times, this may indicate insufficient quality.)

 Use a checklist or ranking tool:

Note: If you edit or update a validated hedge, or apply it outside its tested database or subject area, it is no longer considered validated – so you cannot guarantee the level of sensitivity and/or precision.

Guidelines and standards

'If published approaches such as search filters … or search strategies from other systematic reviews, were used, cite them. If published approaches were adapted … note the changes made.' - PRISMA 2020 Explanation and Elaboration, p. 7

Other standards

Sources of hedges / filters