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Conducting a Literature Review

A collection of strategies and resources for conducting a literature review

Search Strategies

Once you have identified the key concepts of your research question (see "Developing a Question"), you can use those concepts to develop keywords for your search strategy. The following tips and techniques will help you design a precise and relevant search strategy.

Keywords are any words you might use to search the record of an article, book, or other material in library databases. The database searches through the metadata (such as title, authors, publication, abstract, etc.) to find resources that contain the word you searched, and may also search through the full text of the material.

Keywords are most successful when you're searching for the words that the authors use to describe the research topic, as most databases will search for those specific words within the record of the article. To increase your chance of returning relevant results, consider all of the words that might be used to describe the research you're trying to find, and try some of these out in sample searches to determine which words return the best results.

Search Tips - Keywords

  • Search for singular and plural terms together: (physician OR physicians)
  • Search for both the American and British spelling of words: (behavior OR behaviour)
  • Search for synonyms of terms together: (teenager OR adolescent)
  • Search for phrases inside of quotation marks: ("young adult")

Use Boolean operators to combine keywords for more precise search results. 

AND - If the term must be included in your search:

influenza AND vaccine

OR - If terms are interchangeable, i.e. synonyms. Place OR'd terms within parentheses:

(influenza OR flu) AND vaccine

NOT - If a term should not be included in your search. This Boolean operator is rarely necessary for literature reviews.

(influenza OR flu) AND vaccine NOT H1N1


Note how we've used parentheses in the examples above. Search strings like these are similar to mathematical equations, where you perform the actions within the parentheses before proceeding from left to right to run the search. For example, using the search [(influenza OR flu) AND vaccine] will find results that have a term relating to influenza/flu, as well as the term vaccine.

If we moved the parentheses, it would be a very different search. [influenza OR (flu AND vaccine)] will provide results that use the term influenza, as well as results that use both the terms flu and vaccine. This means you would get results having to do with influenza but perhaps nothing to do with vaccination. 

Here are a few examples of how this search would be different depending on the arrangement of booleans and keywords. The area highlighted in pink represents the search results that would be returned with this search.

(influenza OR flu) AND vaccine

flu OR (vaccine AND influenza)

(vaccine AND influenza) OR (influenza AND flu) OR (vaccine AND flu)

Truncation allows you to quickly include all variations of a word in your search. Use the root of the keyword and add an asterisk (*). For example:

nurs* = nurse, nurses, nursing, nursery

IMPORTANT: Notice that "nursery" is also retrieved in the above search. Truncation will save you from having to include a large number of synonyms, but it will also add a certain number of irrelevant results. You can limit this effect by using the NOT Boolean operator, i.e. NOT nursery.

Wild cards allow you to replace a letter in a keyword to retrieve all variations of the spelling. For example:

p?ediatric = pediatric, paediatric

Free-Text vs. Thesaurus Searching

While you can search any word as a keyword, databases also contain an official list of the terms they use to describe the subject of each article, called Subject Headings. You can look up Subject Headings in the thesaurus of the database, using the thesaurus's search box to pull up the recommended Subject Heading for a given keyword. When searching specifically for Subject Headings, the database will only search the Subject Headings field within the record of each article (ie, not the title, abstract, etc.). This is a much more targeted method of searching, and is an excellent addition to your search strategy. 

A strong search strategy will use both free-text (keyword) searching and thesaurus searching, to ensure that all relevant articles have been retrieved by the search. The lists below outline the strengths and weaknesses of both types of search strategies.

Free-Text Searching
  • Natural language words describing your topic
  • More flexible search strategy - can use any term in any combination
  • Database looks for keywords anywhere in the record - not necessarily connected together
  • May yield too many or too few results
  • May yield many irrelevant results
Thesaurus Searching
  • Pre-defined "controlled vocabulary" words used to describe the content of each item in a database
  • Less flexible search strategy - need to know the exact controlled vocabulary term
  • Database looks for subjects only in the subject heading or descriptor field, where the most relevant words appear
  • If too many results, you can use subheadings to focus on one aspect of a broader topic
  • Results are usually very relevant to the topic

MIT Libraries. Database Search Tips: Keywords vs. Subjects.

Each database has their own thesaurus. You will need to adapt your search strategy for each database to take advantage of their unique thesaurus.

PubMed uses MeSH terms (Medical Subject Headings). You can learn more about finding and using MeSH terms here:

CINAHL uses CINAHL Headings. You can learn more about finding and use these terms here:

In other databases, look for a link with the terms "headings", "subject headings", or "thesaurus" to find the appropriate thesaurus terms for your search.

Citation Searching

Citation searching is a search strategy that allows you to search either forward or backwards time through the literature based on an identified relevant article:

You can search forward in time by using databases that allow you to search for other articles that have cited the identified relevant article. (Web of Science and Google Scholar can do this automatically.)

You can search backward in time by reviewing the reference list of the identified relevant article for additional article citations.

For more information about how to perform citation searches, check out this guide from the University of Toledo Libraries:

Retrieving Materials

1. Use the Health Sciences Library website to select a database for your search.

2. Conduct your search and select relevant article(s).

3. If Full Text is available within this database, select "PDF Full Text" or similar button.

4. If Full Text is not available within this database, select "Find it at WSU" button. This will either bring you into the library catalog to (1) select the available database or (2) request the item using the "Request Item" button; or straight into the available database.

Click Find It At WSU


Click Database Link from Catalog


Click Request Item if unavailable


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