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PubMed: Combining Terms

Boolean Logic: AND, OR, NOT

To add terms to your search you can use the Boolean operators AND, OR or NOT.

AND: Citations retrieved include all of the terms.

Using AND will retrieve fewer results because both terms must be present in the citation.

Venn diagram visualizing boolean operation for e-coli AND salmonella. The center of the venn diagram is filled in because this search finds both terms

e-coli AND salmonella

 

OR: Citations retrieved include either term.

Using OR will retrieve more results because either term can be present in the citation.

Venn diagram visualizing boolean operation for anorexia OR bulimia. The entire venn diagram is filled in because this search finds either term or both terms

anorexia OR bulimia

 

NOT: Will exclude a term from your search.

Use NOT with caution as it may exclude relevant results.

Venn diagram visualizing boolean operation for mutation NOT frameshift. The left side of the venn digram is filled in because the search is finding mutation, but excluding frameshift completely

mutation NOT frameshift

Using Parentheses

Using parentheses changes the order in which PubMed processes the search statement. In order to build a more complex search, parentheses can be used around like terms that are combined with OR.

Screenshot showing how to format a boolean search in PubMed using parentheses

It's a good idea to get into the habit of using parentheses every time you combine search terms with OR so that you don't need to remember which way PubMed processes your search.