Types of search

There are two types of search: free-text searching and thesaurus searching, and using a combination of the two can help maximise the chances of you recalling all the most relevant evidence.

Free-text search

A free-text search means the database will find exactly what you type in the search box. This might seem the most simple and easy way to search, but it’s not necessarily the most effective way. You should be aware that free-text searching:

  • Ignores plurals: For example, if you search for ‘dog’ in some databases, you will not retrieve results containing the word ‘dogs’.
  • Ignores spelling differences: For example, a search on ‘animal behaviour’ (the English spelling) will not always retrieve results containing ‘animal behavior’ (the American spelling).
  • Can retrieve too many irrelevant results: For example, a search on ‘nutrition’ will retrieve every instance of this term in every record in the database, regardless of whether it was a focus of the publication.


When searching using free-text search terms it’s important to remember that words you use to mean one thing can have an entirely different meaning in another subject area.  For example, the word ‘membrane’ has a different meaning depending on whether you’re a biologist or an engineer.  This is particularly important if you’re searching a resource which isn’t subject specific, such as Google Scholar.

Thesaurus search

If the database has a thesaurus you should take full advantage of this, as it will automatically retrieve results containing related terms, which you may not have thought of, and will help focus your search.

A thesaurus can be called different things:

  • MeSH (Medical Subject Headings) in PubMed and Medline
  • CAB thesaurus descriptors in Cab Abstracts
  • Subject Headings
  • Controlled Vocabulary
  • Keywords

One of the most common mistakes in veterinary searches, is that the thesaurus term for the Species was not used, and so a large number of relevant papers are missed.  For example, a search on horse in Medline, will not retrieve records that use the plural horses.  However, a search on the thesaurus term horses will retrieve records that contain any of these terms:

  • equus przewalskii
  • domestic horse
  • horses
  • domestic horses
  • horse domestic
  • horse
  • horses domestic
  • equus caballus

Combine free-text and thesaurus searches

It is recommended practice to run both a free-text search and a thesaurus search for each of your key concepts and then to combine the two searches with the Boolean operator OR.  This will maximise the chances of you retrieving all the most relevant evidence for that concept.

If you go back to our example of a search strategy you can see an example of how this can be done.