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KNH 409/509 - Nutrition for Sports and Fitness: Searching the literature

New to searching for literature?

This series of short videos will show you a few useful techniques you can use to improve your literature searches.


Boolean and other operators

Operators are symbols or words that, when combined with search terms, help to either limit or expand your searches. They are important tools for streamlining the search process, but they can be tricky to use correctly and effectively. Here are some common operators and general rules for using them.


Boolean operators

Boolean operators are used to define the relationship between search terms. They can be used to broaden or narrow a set of search results. There are three common Boolean operators: AND, OR, and NOT. It's good practice to capitalize Boolean operators because some databases require it.

AND is used to join words or phrases when both (or all) the terms must appear in the items you retrieve.

This search query would return a much smaller set of records, and the items found would be more specific to your research question. If you are retrieving too many records, try adding another search term with the Boolean Operator AND.

animated Venn Diagram of AND boolean search

OR is used to join synonymous or related terms, and instructs the search tool to retrieve any record that contains either (or both) of the terms, thus broadening your search results.

The OR operator is particularly useful when you are unsure of the words used to categorize your topic or if information on your topic is even available. If you are retrieving too few records, broaden your search by adding a synonym with the Boolean Operator OR.

animated Venn diagram of OR boolean search

NOT is used to exclude a particular word or combination of words from your search results.

If you are retrieving many records that are unrelated to your topic, try using the NOT operator to eliminate a word. This should be done cautiously, because as well as deleting the unwanted items, such a search will also eliminate records that discuss both the relevant topic as well as the unrelated topic.

animated Venn diagram of NOT boolean search




Truncation is used to search all terms that begin with a common stem. Databases tend to be very literal in interpreting your queries, and, for example, won’t return plurals of words if you just type in the singular form (some search systems are capable of doing this automatically, but you can’t assume). If a term you are searching has variants with the same beginning but various suffixes or endings, use truncation to capture all these. The symbol most commonly used for this is an asterisk. For example:

comput* = computer, computing, computation…

Use the asterisk to replace the last few letters of the word. The asterisk means “any character(s) (or none) can be here.” Be careful where you truncate – in the above example, truncating back to comp* would give back a mess of different things (e.g., competition), while compute* would eliminate some of the relevant variants.

Be careful with this technique! It can backfire pretty easily. Do not try to truncate short words like cat or rat, as you’ll bring back too much irrelevant stuff, like catastrophe. Instead search on the particular variants you need, e.g. cat OR cats. Also note that you cannot truncate “backwards” – computers* isn’t a very useful construct, as no other words begin with “computers”.


Phrase Searching

In many databases it is possible to search for sets of words immediately adjacent to each other, i.e. phrase searching. How this works depends on the database. In some, typing two or more words together, e.g. house cat, implies searching for the words together. In other search tools (including Web of Science, and Google), searching on the two words means the same as a Boolean AND search, e.g. house cat is the same as house AND cat; while putting the phrase in quotation marks demands the terms be searched as a phrase, e.g. “house cat”. Consult the database help, or try these possibilities and see what you get.

Best practice is to use quotations around the phrase you want to search. Most databases will recognize this as a phrase search, even if it doesn't require it, and you'll develop a good habit for the databases that do require it.