How to Write a Literature Review: Boolean Operators

• Databases require mathematical rules in order to function
• These mathematical functions are known as Boolean Operators
• There are different operators, the most commonly used are AND, OR, NOT
• Boolean operators allow for the combination of concepts in databases
  • OR expands a search
  • AND focuses a search
  • NOT removes from a search

• When searching you sometimes need to think of synonyms for a concept in order to capture all the information on that concept
• For example, to capture all the information on heart attacks you would search:
  • heart attack [1] OR myocardial infarction [2] OR cardiac arrest [3]
• The Venn diagram below illustrates how 3 sets of information, combined using OR, gives you all three sets of information in your results

What to watch for: do not overdo it when it comes to synonyms, only use the most logical; do not include broader concept terms, this will take away the focus of your search.

• AND is used in searching when you want the results to contain all the concepts important to your research
• For example, to capture information on the use of exercise by an elderly population as part of a fall prevention program you would search exercise AND elderly AND fall prevention
• The Venn diagram below illustrates how 3 sets of information, combined using AND, would give you one set of information: (exercise [1], elderly [2] , fall prevention [3]); only the small centre set of information would be in your results, the one that contains all three elements

What to watch for: be careful of having too many concepts, if you AND too many ideas together you will end up with zero results

• NOT narrows your search, telling the database to ignore concepts that may be implied by your search terms
• For example:  if you were searching for articles on nursing and education classes but you did not want articles on breast feeding would search: (nursing [1] AND "education classes [2]") NOT "breast feeding [3]" 
• The Venn diagram below illustrates how you would use NOT to exclude information from a search, you would retrieve information that contains (nursing [1] and education classes [2]), the arrow head shaped set in the middle; the set (nursing [1], education classes [2], breast feeding [3]) would be excluded from the results

What to watch for: be careful using NOT as you may inadvertently exclude helpful articles from your search

• Databases follow the commands you type in and return results based on those commands.
• Databases follow a specific logical order when using Boolean operators: 
  • Databases usually recognize AND as the primary operator, and will connect concepts with AND together first.
  • If you use a combination of AND and OR operators in a search, you must enclose the words to be "ORed" together in parentheses so the database will combine those as a set before combining the AND concepts together.
• Examples:
  • ethics AND (cloning OR reproductive techniques)
  • (ethics OR morals) AND (bioengineering OR cloning)
  • (nursing AND education classes) NOT (breast feeding)

Searching Basics

1. Create a Searchable Question
2. Boolean Operators
3. Search Strategy
4. Subject Headings and Keywords
5. Phrases
6. Truncation
7. Fields
8. Limits

Consult a Health Sciences Librarian