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Nursing & Health Services Research Guide

Boolean Searching

Boolean logic (named after mathematician George Boole) is a system of logic to designed to yield optimal search results. The Boolean operators, AND, OR, and NOT, help you construct a logical search. Boolean operators act on sets -- groups of records containing a particular word or concept.

The circle diagrams that help illustrate the relationships between the sets used in Boolean logic were named after another mathematician, John Venn. (The shading represents the outcome of the Boolean operation.)


When terms/concepts are combined with the AND operator, retrieved records must contain all the terms. For example: "Does taking aspirin cause Reye's Syndrome in children?" This will retrieve citations that discuss all three concepts in each article. The more concepts you AND together, the fewer records you will retrieve.


Boolean AND Operator


The Boolean operator OR allows you to broaden a concept and include synonyms. For example, kidney disease OR renal diseases will retrieve citations using either (or both) terms. This expands your search by retrieving citations in which either or both terms appear. The more concepts or keywords you OR together, the more records you will retrieve.



Boolean OR Operator


The final Boolean operator NOT allows you to exclude concepts not relevant to your search. For example, you could search multi-infarct dementia by using Dementia NOT Alzheimer's



Boolean NOT Operator

But be careful using this because you would eliminate records discussing both types of dementia, as all articles discussing Alzheimer's are eliminated.

Text/Images courtesy of University of Minnesota Health Sciences Libraries Bio-Medical Library

Developing a Search Strategy for Library Research Tools

When searching the library research databases or OneSearch, it's good to have a strategy. Unlike Google or Internet search engines, the databases and OneSearch can't interpret questions pasted in, natural language or strings of unconnected words. You should identify the key concepts in your thesis or research question and then brainstorm for a few alternative terms and synonyms that go along with them. Then you can connect and combine those terms in different ways using Boolean (see other boxes on this page).

For example, what if you were researching the question:

What are the attitudes of nurses towards working hours?

The key concepts are obviously the words I underlined:

attitudes    nurses    working hours   


It's good to have a few synonyms and related terms for your key concepts. They may also be helpful in your search!

attitudes: nurses: working hours:
views, perceptions, beliefs, bias, opinions, response, surveys, questionnaires nursing staff, nurse practitioners, nursing students, etc. shifts, shift system, working shifts, night hours, flextime

Now I can develop either a basic search statement:

attitudes AND nurses AND working hours

Or a more advanced search statement, throwing in some related terms and synonyms, nested in sets of parentheses and connected by OR:

(attitudes OR surveys) AND nurses AND ("working hours" OR shifts)


Find out why I combined terms with AND and OR in the "Boolean Searching" box to the right (capitalization and bold type just for emphasis)!

Boolean: Combining Keywords

This YouTube video from the University of Auckland, New Zealand demonstrates how to combine search keywords using the Boolean AND, OR, and NOT. It also shows you how Boolean works in a variety of database and search tool screens.