Search Strategies: Keyword vs. Subject Searching

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