Introduction to Boolean Logic

In the context of database searching, Boolean logic refers to the logical relationships among search terms.

• The Boolean operators AND, OR, NOT can be used to combine search terms in PubMed.
• In PubMed, Boolean operators must be entered in uppercase letters.

OR:

• Used to retrieve a set in which each citation contains at least one of the search terms.
• Use OR when you want to pull together articles on similar topics.

Example:   football OR hockey OR soccer

Each circle in the diagram to the right represents the retrieval for each term. The grey areas represent the retrieval for this example – all records that include any one of these terms.

The table below represents sample results for each term, then for the terms combined with OR.