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Complementary and Integrative Health

Boolean Operators

"Boolean operators" are the connector words that are used to combine sets of search results to achieve certain desired effects. They are named for George Boole, a 19th century English mathematician. The most commonly used Boolean operators are AND, OR, and NOT.

Here is a handy "rule of thumb" for the Boolean operators AND and OR:

  • Use AND when you want to find articles that contain ALL terms/concepts. Combining sets with AND will produce a smaller set, since all items in the set must contain all terms.
  • Use OR when you want to find articles that have ANY of the terms/concepts. Combining sets with OR will produce a larger set ("OR makes more"), since the items in the set must contain only one of the terms.

For more information about Boolean operators, check out these resources:

  • this link from U Mass Boston, which includes a 2-minute video

Too many results?

This can be as much of a problem as getting too few results. Try one of these strategies to simultaneously reduce the numbers of hits, and focus the results:

  • add another search term, using the Boolean operator AND to make a smaller set
  • search on a more specific term
  • in databases that offer this feature, such as MEDLINE, restrict your search to MeSH Major Topic
  • in databases that offer this feature, add one or more subheadings
  • apply one or more filters, such as publication date, article type, or age group
  • when available, deselect the Explode feature, and search only on the more general term, or choose a more specific term on which to search

Too few results?

Well, this can be a problem indeed! Here are some tactics to try:

  • check your spelling!
  • remove one or more terms from your search query
  • search on related terms or synonyms, combining terms using the Boolean operator OR to make a larger set
  • substitute a more general term
  • remove filters, or apply them incrementally
  • when available, use the Explode feature to search on narrower terms as well as the more general term