What are Boolean Operators?

If you have ever Googled something, you have already created Boolean search strings. If you use it without realizing it, you can learn a few Boolean operators that will drastically improve your current sourcing efforts.

Boolean Operators

  1. AND
    Narrows your search results to include only relevant results that contain your required keywords (e.g. Alzheimer's AND target will only yield documents that have both of those keywords).
  2. OR
    Expands your search results so all results must contain at least one, if not more, of your defined keywords or phrases. OR is useful for two scenarios: (1) you need to include all synonyms for a given title, phrase or word (e.g. interleukin-1 OR IL-1 OR IL1), or (2) creating a list of all possibilities where you only need at least one of the keywords to be returned (e.g. Merck OR Pfizer OR Novartis).
  3. NOT
    Limits your search by excluding defined keywords and/or phrases from your results (e.g. drug NOT vitamin reveals all results that discuss drugs, excluding those that also mention "vitamin").
  4. "Quotation Marks"
    Use quotes around a phrase that needs to be returned in that exact order. For example, "United States of America" will yield results with that exact term, but without quotes, each word in the phrase will be treated separately, as if you used OR between each word (United OR States OR of OR America).
  5. (Parenthesis)
    Parentheses are used to give priority to the keywords contained within over the other elements around it. As a rule of thumb, parentheses should be used around OR statements, ensuring the search engine properly resolves the OR statement before moving on to other operators. For example, (Tumor OR Carcinoma OR Cancer) AND treatment will yield results that mention treatment and any one or several of the key terms in parenthesis.
  6. Asterisks*
    * on a term matches multiple characters preceding a stem. For example, hydroxych* yields results for hydroxychloroquine, hydroxycholesterol, etc.
  7. Question Mark?
    ? on a term matches a single character preceding a stem. For example, a?duction can yield results for abduction and adduction. Another example can be anemi? to find results for anemia and anemic.
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