Boolean Operators can be defined as a connecting or combining of two or more concepts together to indicate a relationship. Most searchable databases and/or search engines recognize these logical operators as AND, OR, and NOT. When used effectively one can develop a strategy for a particular end result.
AND is used as a Boolean operator to instruct the system to display only those references in which BOTH terms are present
Use of the Boolean operator AND tends to increase precision and reduce recall. For example, AIDS AND tuberculosis will retrieve fewer citations than either term individually, because it requires the system to retrieve only those items that contain BOTH concepts.
OR is used as a Boolean operator to retrieve references in which the terminology of authors may include synonyms or multiple terms that the system should accept as pertinent for your search.
Nesting is a technique to use AND to combine terms OR to compare/contrast. An example of this approach would be comparing the use of drugs cipro, penicillin in treating respiratory infections. Your search strategy would look like the text below; parentheses are used to separate the strategy into two subsets and the two Boolean operators.
(penicillin OR cipro) AND respiratory infection
Use of the Boolean operator NOT can be used to eliminate certain aspects of a concept. For example, AIDS NOT sarcoma will retrieve citations that don’t include sarcoma. This can cause the system to excluding relevant articles so use with caution.
Remember that the connectors AND and NOT generally limit your search (decreases the number of citations) and the connector OR expands it (increases the number of citations). So the following strategies naturally follow:
If you are retrieving too many records on your topic, try adding another search term with the connector AND
If you are retrieving too many records on an unrelated topic, try eliminating a word with the connector NOT
If you are retrieving too few records on your topic, try adding another search term with the connector OR
