Boolean operators are named for George Boole (1815-1864), an English Mathematician and Philosopher. Boolean Algebra and Symbolic Logic both derive from his work. Boole is generally considered the father of modern computer science. Most electronic indexes (databases) require the use of Boolean operators in parsing search terms, although this is not always apparent. Boolean search statements are incredibly powerful in retrieving what you need provided:
Rather than typing a full sentence or question into a search box, using Boolean operators can help you create an efficient and effective database search.
Try our new Search Strategy Builder, which will add Boolean operators to create searches out of keywords that you supply!
AND: narrows search results; both terms that you connect with AND must be somewhere in the bibliographic record for that record to be retrieved. AND narrows a search and retrieves fewer articles. For example:
stroke AND paralysis
--> search results must include both terms
OR: only one of the search terms combined with OR is required for the bibliographic record to be retrieved. OR broadens a search and retrieves more articles. For example:
stroke OR ischemia OR brain infarction
--> search results must include at least one of these terms
NOT: excludes a particular subset, category, or term. NOT requires the presence of one search term and the exclusion of another.
ischemic stroke NOT hemorrhagic stroke
--> eliminates search results terms on hemorrhagic stroke but includes results on ischemic stroke
Learn more about Boolean searching at the PubMed Boolean Tutorial.
Tips & Tricks for Database Searching
Truncation: A symbol, specific to the search interface, which allows the retrieval of all endings for the specified base word. An asterisk (*) is often used. For example, child* would retrieve records with children, childish, childhood and every other word that begins with the root word "child."
Wildcard: A symbol, specific to the search interface, which allows the retrieval of various spellings of a word. A question mark is often used. For example, wom?n would retrieve records with women and woman.
Quotation marks: To search for an exact phrase with the words together, in the order you wish to find them, add " " quotation marks around the phrase, such as "physical activity" versus finding an article about physical education and an activity for elementary school students.
Parentheses: Help to keep search terms together, such as searching for synonyms of a concept while also searching with another Boolean operator, such as measles AND (epidemic OR "disease outbreak")
Example Boolean search statements using symbols & parentheses:
child* AND anxiety AND (exercise OR "physical activity")
Ischemia AND (Stroke OR Infarct)
alzheimer* AND malnutrition AND elderly
alzheimer* AND malnutrition AND (elderly OR aged OR older adults)
alzheimer* AND (nutrition OR diet OR malnutrition) AND (elderly OR aged OR older adults)
(delirium AND surgery) NOT mice
Research Database Fields
Default - Most research databases have a default search that looks for your keywords in a variety of places. Depending on the database, this often includes the title of documents in the database, the abstract (summary) of the documents, and the 'subject headings,' or 'index terms' that the database creators have used to tag the documents in the database. *However, a database's default search may also look in: the journal / source title, the full text of documents included in the database, document reference lists, and other areas.
Title / Document Title - Target your search to those documents that have your keywords in their title.
Abstract - Target your search to those documents that have your keywords in their abstract / summary paragraph.
Title & Abstract - Target your search to those documents that have your keywords in their title.
'Subject Headings' / 'Index Terms' - Target your search to those documents where your keywords match up with the index terms or subject headings (in PubMed - MeSH - Medical Subject Headings) that the database creators have used to tag the documents with a significant focus on that topic or topics.
To search results on a specific website, type site: (no spaces) and the name of the website as well as your search term(s). You can also search for a specific site domain, such as .gov.
Use the AND and OR Boolean operators
Instead of NOT, use the - symbol (no space after the symbol)