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Nursing Research Guide: Boolean Operators

Identifying Concepts & Building a Search

It is helpful to create a diagram of the important concepts for your topic as shown below.

Question: How effective is a day care service for individuals with dementia or alzheimer's disease in alleviating caregiver burden?

Notice that non-essential words such as "service" and "individuals" and "alleviating" have been removed from the strategy. You could also leave out the word "effective" unless the search results set is extremely large. For each additional term that you add to your search with the Boolean operator AND, the results will become smaller.

This search could be entered in PubMed as:

day care AND (dementia OR alzheimer's) AND caregiver burden


Boolean Tips Sheet

An excellent guide to using Boolean operators in a database search is available from the University of Minnesota Libraries.

Boolean Operators

About Boolean Operators

The Boolean operators AND, OR, and NOT are used to combine search terms in databases.

  • In PubMed, Boolean operators must be entered in UPPERCASE letters
  • Use Boolean operators when searching for more than one concept or when combining two or more search statements

Combining Concepts with "AND"

Example: dementia AND day care

The Boolean operator AND will retrieve citations that contain both concepts "day care" and "dementia" in the same record (note the dark grey segment). As a result, you will retrieve fewer records.

Combining Concepts with "OR"


Example: dementia OR alzheimer's

The Boolean operator OR will retrieve citations that contain either "dementia" or "alzheimer's"  in the records (as shown by the entire shaded areas of both circles). As a result, you will retrieve a larger number of records.

Combining Concepts with "NOT"


Example: dementia NOT alzheimer's

The Boolean operator NOT will exclude citations containing the second term (as shown by the shaded area of the first circle.) Use NOT cautiously because you may exclude some records that could be relevant to your search.