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Keyword vs. Subject Searching

Search terms are extracted from your research question (such as the terms that may up your PICO) and can be entered into whichever database(s) you decide to use. Databases give you the option of using keywords or subject headings. 

Each database has its own set of subject headings, designed specifically for the literature from the field(s) of study the database contains. Knowing the difference between keywords and subject headings, as well as the advantages and disadvantages for both of them, can help you perform better searches.

Keyword searching is how you typically search web search engines.  Think of important words or phrases and type them in to get results. 

  • Natural language words describing your topic - good to start with 
  • Flexible and able to be combined in any number of ways
  • Searches for matching words or phrases anywhere in the records the database contains (such as title, abstract, journal title)
  • Sometimes either too broad or too narrow, resulting in either too many or too few results
  • Reflective of recent phenomena in advance of when the subject headings are added
  • Sometimes either too broad or too narrow, resulting in either too many or too few results
  • Reflective of recent phenomena in advance of when the subject headings are added

Subject headings describe the content of each item in a database. Use these headings to find relevant items on the same topic.  

  • Pre-defined, "controlled" vocabulary used to describe the content of a text found in a database (such as PubMed MeSH or CINAHL Subject Headings).
  •  Less flexible and must be chosen from the thesaurus used by the database; if the incorrect subject heading is selected, none of the results will be relevant.
  • Database looks for subjects only in the subject heading or descriptor field, where the most relevant words appear 
  • Helpful for retrieving a set of articles with fewer irrelevant results
  • Slow to change--this means that the most recent changes in knowledge--on diseases, drugs, devices, procedures, concepts--may not be reflected in the controlled vocabulary.

Keyword or Subject Heading Search?

Some basic guidelines are:

  • If the term or topic is very recent, keywords may be the best option
  • If no Subject Heading exists for your term, or seems inadequate, use a keyword
  • If the keyword is too vague or broad, a Subject Heading may help focus your search and eliminate too many results
    • e.g. neuroses would be a very broad keyword search
  • If you want a very comprehensive literature search, you should use both a keyword and a subject heading
    • e.g. Heart attack OR Myocardial Infarction


Use the filters in each database to narrow your search down and eliminate irrelevant results. These helps to maximize your search process by making it more efficient. 

Limiting to a specific year range and peer reviewed articles are the most commonly used filters.

Other helpful filters include by full text availability, study type, population group as well as more specific filters such as "Randomized Control Trials' and "Evidence Based Practice." Filters vary according to database. Typically, you can find filters either on the Advanced Search page, underneath the search boxes or on the left-hand side of search results. These two databases go over in greater detail how to use certain filters in individual databases: Evidence-Based Practice and Quantitative and Qualitative Research

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