After you have clearly identified your research problem and found out the relevant subject terms that you will base your search on, you should think about how to combine these search terms. Most databases allow you to combine search terms in various ways by means of the Boolean operators AND, OR and NOT.
Combining query terms using AND
When you combine your query terms by using AND, the resulting hits will contain documents that deal with both terms. The AND operator aims at focusing the search and narrowing down the number of hits.
When you search for decubitus AND prevention, the resulting hits will contain only documents that deal with both decubitus and prevention as shown in the diagram below.
Combining query terms using OR
When you choose to join two query terms with the OR operator, you get a search result that contain either one of the terms, or both. Combining search terms with OR thus generates an extended search result with a larger number of hits. The OR operator is usually employed to cover alternatives or synonyms of the query term. For example, the search for decubitus OR bedsore, will give a hit that contains either decubitus or bedsore, or decubitus and bedsore as shown in the diagram below.
Combining query terms using NOT
When you combine your query terms with the operator NOT, your search result will consist of only one of the terms, and the other term will be eliminated from the search. Since the use of NOT eliminates a large number of hits, it should be used with caution. For example, when you search for decubitus NOT prevention, your search result will contains only instances of decubitus, and all documents that deal with prevention will be filtered out from the search.
Last updated: December 1, 2014