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Systematic Reviews for Health: 3. Develop Search Terms - Free-Text

A guide on how a Research Librarian can help you during a systematic review process

Develop Search Terms

The Cochrane Handbook, 4.4.4 suggests searches should comprise a combination of subject terms selected from the controlled vocabulary or thesaurus (‘exploded' where appropriate) (see Step 4) with a wide range of free-text terms in order to identify as many relevant records as possible searches.

  • If you use keywords only, you could miss articles that do not use your precise terms.
  • If you use controlled vocabulary only, you could miss articles that have not been indexed yet or have older indexing.

Step 3. Free-Text Terms

Determine any alternative terms for the identified key concepts and add them to the Concept Table. It is important to enter as many potential terms as possible. Some authors may refer to the same concept using a different term. Important articles may be missed if not all relevant alternative terms are included in the search.

These free-text terms will be searched as textwords (words in title, abstract, author's keywords).

Ideas For Brainstorming Free-Text Terms

  • Conduct a simple search on the topic – look at words in titles, abstracts and author's keywords
    • Scan for synonyms, alternative spelling variants, acronyms, abbreviations, medical terms, laymen's terms, drug brand names, and alternative ways of ordering phrase words
  • Initial literature scanning of core articles and/or similar systematic reviews – look at titles and abstracts and author's keywords
  • Speak to an expert in the field / supervisor
  • Subject headings need to be repeated as free-text terms
  • Look at Entry terms, Used for terms, Related terms mentioned in the subject heading databases (e.g. MeSH, Emtree, CINAHL Heading databases) (see Step 4). Often one or a combination of a few words is enough to capture many entry terms.
  • For an 'exploded' subject heading, include narrower subject headings found in the hierarchy as free-text terms
  • Google or a dictionary may identify additional terms
  • Check for existing search strategies, e.g. subject search filters (see Subject Search Filters)
  • Text mining (frequency analysis to inform search term selection; identifies commonly appearing words in pre-identified relevant studies)
    • WordFreq from Systematic Review Accelerator - single words and phrases (upload EndNote library with key studies saved as XML file)
    • PubMed PubReMiner - good for single words (run PubMed search)
    • TerMine - good for phrases


This Concept Table lists alternative terms for the four concepts in our example. These terms were identified by scanning the titles and abstracts of retrieved articles of an initial basic search.

Concept 1 Concept 2 Concept 3 Concept 4






Animal-assisted therapy

Animal-assisted activities

Animal-assisted interventions

Animal therapy

Pet therapy

Dog therapy

Dog-assisted therapy

Canine-assisted therapy

Pet-facilitated therapy


Music therapy




Auditory stimulation



Apathy inventory

Cornell scale

Cohen Mansfield





Study designs to be included: RCTs only (see Step 8)

See source of example

Subject Search Filters

There are various web sites listing search filters for subject searches. You may not want to fully rely on these search strategies, but rather use them as a starting point to gather ideas.

If you use somebody else's search strategy, you should acknowledge this. For example, you could cite it in the methods section, where you broadly describe how you conducted the search. Then add it to the reference list like any other type of reference.

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