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The EBM Medical Literature Search

What are Boolean Operators?

Boolean Operators ( AND, OR, NOT) are commands used to make your search strategy more concise. In it's most simple use, library databases are searched effectively by linking two keywords with a Boolean Operator. This page covers AND, OR, NOT in both simple and advanced searches. For advanced searches, Boolean Operators are combined with symbols and Order of Operation to create Nesting. Nesting examples are included on this page but will also be covered in this advanced section under the tab "nesting." 

Boolean Operators

Image depicting Boolean AND


Use "AND" to link two terms together, this narrows your results. Articles will contain both and omit the pieces that only have one term or the other.

When you start to nest Boolean terms, AND is seen as the primary operator, and will be factored before OR and NOT. 

An example of  AND would be these different searches: 

  • Fever AND Joint Pain (4,432 results) 
    • Fever + joint pain (may or may not be next to each other) 
  • Fever AND "Joint Pain" (780 results) 
    • Fever + "joint pain" (exact phrasing) 
  • (Fever AND joint pain) OR chills (16,774 results*)
    • Fever + joint pain
    • Chills
  • Fever AND (joint pain OR chills) (8,064 results) 
    • Fever + joint pain
    • Fever + chills
    • Fever + joint pain + chills

*Results run as a Pubmed search on 4/6/2021. 

Image depicting Boolean OR


Use "OR" to look for articles that contain both words. This generally broadens your results; articles will contain either term or both terms. Used with nesting, such as quotations, this strategy can help narrow a broad result. 

OR can be seen in the AND example box on this page but here is another one:  

  • Fever OR joint pain (317,869 results*)
    • Fever
    • Joint + pain (may or may not be next to each other) 
  • Fever OR "Joint Pain"  (238,009 results) 
    • Fever
    • "Joint Pain" (exact phrasing)
  • Fever OR joint AND pain (111,520 results) 
    • Fever and pain
    • Joint and pain

*Results run as a Pubmed search on 4/6/2021. 

Image depicting Boolean NOT


Use "NOT" to look for articles that do not contain a specific word. This narrows your results. 

Using NOT may negatively effect your results, as it ignores all articles with the undesired word. This operator is best used after you have gained some familiarity with the literature and notice a topic trend you wish to ignore, or if you already know you do not wish to look at a particular portion of the literature.


An example of NOT in action* would be: 

  • Typhoid fever NOT children (10,758 results)
    • Typhoid fever - children
  • Typhoid fever NOT children OR elderly (5,613,679 results)
    • Typhoid fever - children
    • Elderly
  • Typhoid fever NOT (children OR elderly) (9,923 results) 
    • Typhoid fever - children
    • Typhoid fever - elderly

*Results run as a Pubmed search on 4/6/2021.

Photo Attribution

Created by Tiffany Follin using Piktochart

Last updated on Apr 23, 2024 3:12 PM