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The next step in the literature search process is figuring out how you will combine your keywords. You won't be able to just toss all of them together into a search box and call it a day. The research databases require a little more direction than that. The best way to search is by combining your keywords into search strings using Boolean operators. Simply put, Boolean operators tell the database how the keywords you're searching for are or are not related. The operators you'll want to become familiar with are OR, AND, and NOT. (Note: you don't have to capitalize your operators when you go to type in your search strings, but it can help visually separate your terms and is highly recommended.)
| Boolean operator | When to use it | Example search string | What it does |
|---|---|---|---|
| OR | Use OR when you want to search for synonyms or similar concepts | respiration OR breathing |
Will bring back results that mention either "respiration" or "breathing". Will increase the number of search results; search is more comprehensive. |
| AND | Use AND when you want to connect two or more concepts | respiration AND salamander |
Will only bring back results that mention "respiration" together with "salamander" (but not necessarily adjacent to each other). Will decrease the number of search results; search is more focused. |
| NOT | Use NOT when you want to exclude a concept from your search results. Use very sparingly or not at all! | salamander NOT frog |
Will bring back results that mention "salamander" but will exclude those that mention "frog". Best to use only if you notice the same irrelevant concept coming up in your search results, as it may potentially exclude some relevant information. Will decrease the number of search results. Order matters with this one! salamander NOT frog will bring back a different set of results than frog NOT salamander. |
There are lots of other techniques you can use to effectively and efficiently search literature databases. Most will allow you to use all the techniques listed below but may have slightly different characters or syntax. Be sure to check the databases' help pages to find the correct syntax for each resource!
| Strategy | What it does | Example |
|---|---|---|
| Truncation |
Uses an asterisk to search for results that include the selected prefix with any word endings VIDEO TUTORIAL: How to Search: Truncation |
nurs* Will include results that mention "nurse", "nurses", "nursing", etc. |
| Wildcards |
Uses a symbol (most often $ or #) to search for terms that may have alternate spellings or additional characters. Check the help page for the database you're searching to make sure you're using the correct symbol. |
an$esthesia Will include results that mention "anesthesia" (American spelling) or "anaesthesia" (British spelling) |
| Phrase searching |
Uses quotation marks to enclose a group of terms that must show up exactly as typed. VIDEO TUTORIAL: How to Search: Phrase Searching |
"cancer fatigue" Will only include results that mention "cancer fatigue" exactly (but not necessarily "cancer-related fatigue"). |
| Proximity searching |
Uses an operator and a number (e.g., "N3", "NEAR/3") to find terms that appear in close proximity to each other. Some databases, like PubMed, do not allow for proximity searching, and others use different syntax. Be sure to check the help page for the database you're searching to make sure you're using the correct syntax. VIDEO TUTORIAL: How to Search: Proximity Operators |
blood N3 collection Will include results that mention "blood collection", "collection of blood", "blood was collected", etc. |
| Nesting |
Uses parentheses to group terms and more effectively use Boolean operators. VIDEO TUTORIAL: How to Search: Boolean Operators (starting at 2:09) |
(cancer OR neoplasm) AND (chemotherapy OR radiation) Will return search results that mention "cancer" together with either "chemotherapy" or "radiation", as well as "neoplasm" with either "chemotherapy" or "radiation". |
| Subject headings | Uses predefined subject terms (also called controlled vocabulary) to help account for different spellings, synonyms, and other related concepts. Typically more limiting than keyword searching. Different databases use different terms, so be sure to check the resource's thesaurus to select the best headings. |
"dementia"[Mesh] Will return search results that have been tagged with the Medical Subject Heading (MeSH) term "dementia". MeSH is used primarily in PubMed; other resources have similar headings. |