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Tips for Searching Article Databases: Combining Terms (Boolean Searching)

Finding the right information isn't just luck. Creating a strategy is essential for successful search results. Knowledge about information resources and search strategies will produce meaningful search results, even when you are not familiar with the topi

Boolean Searching

Search options vary between bibliographic databases, online library catalogs, and search engines. Some resources provide a single search box option for entering terms, and some provide a number of search options, such as a "Quick Search," "Advanced Search," "Boolean Search" or some combinations or variations thereof. "Quick Searches" may have just one box for the search term(s) or there may be a box with a menu of selected record fields that you can choose from. 'Advanced Search' options typically have more than one box for multiple concept terms as well as a menu of all record fields available to choose from. A "Boolean Search" option may be available, either as one of the search options or as part of "Quick Search" and/or the "Advanced Search" that allows one to combine terms utilizing the connector words "AND," "OR," and "NOT" (also known as Boolean operators) to broaden or narrow your search concept. 

Boolean operatives in everyday language may have opposite relationships than when they are used for Boolean search strategies in electronic resources. For instance, in regular speech "AND" means "along or together with," which adds or increases the relationship between the terms, e.g. 5 AND 5=10. In ordinary, daily communication "OR" can be used to connect two concepts so that either one or the other is selected, and thus reduces the end result, e.g. Either this needs to be done OR that needs to be done, but not both.

Boolean Logic

Use "OR" to Broaden Search

In Boolean Strategies, "OR" expands the search to include all records that contain either terms. To broaden your search, think of synonyms and related terms for your search query, and then combine them using "OR." In the example below, a synonym for "fruit fly" might be "Drosophila melanogaster." Keep in mind that some concepts using the same words may be found as individual words and as a single word, for example "bird song" or "birdsong." Truncation may not be possible in such circumstances, but using "OR" to connect the terms will work to pick up either of the terms if they are there. 

Use "AND" to Narrow Search

For Boolean search strategies, "AND" actually narrows the search results. Using "AND" is directing the electronic resources to produce records that include all the search terms that were used—all term concepts that are entered must be in each of the resulting records. The more search terms used, the more specific and thus narrow the results will be. Relevance of the retrieval may depend on the proximity of the words to each other. 

Using "NOT" to Narrow Search

The Boolean connector "NOT" may come in handy, but should be used with care. It is used to eliminate records, as in "anxiety disorders NOT animal" for anxiety disorders related to humans, not animals. But searching with this query would miss a very relevant review Neurobiology of Anxiety Disorders and Implications for Treatment that reviews research on the neurobiology of fear and fear conditioning and "examine its implications fo rthese anxiety disorders with a focus on identifying potential therapeutic strategies" (Garakan, A. Matthew S.J. & Chaney D.S. 2006). This research summary refers to animal studies which form the basis for understanding many human biological conditions, including anxiety. Using the connector "NOT" can exclude significant research from the results. 


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