Free text and controlled vocabulary

It is essential to find all useful search terms, both in free text and in the controlled vocabulary of databases. Use key words from articles central to the issue you want to study. Look at author keywords as well as those set by the publisher. When using free text key words, consider differences in spelling, e.g. between British and American English. Also use both singular and plural word forms. 

colour OR color,             

categorise OR categorize,       

bicycle OR bicycles.

Controlled vocabulary summarizes different synonyms in one term. Articles in a database are indexed - tagged- to describe the article content and make them retrievable. When searching a database with controlled vocabulary, like PubMed, CiNAHL or TRID, use their lists or thesauruses of key words. These lists can be found in separate sections of the databases and can be named differently like MeSH database, CINAHL subject headings, APA Thesaurus of Psychological Index Terms and TRT Transportation Research Thesaurus. 

The illustration below shows the hierarchical structure of the MESH database:



Some databases automatically include the narrower terms when searching for a wider, general term. This function is called "explode". In other databases you must make an active choice to include all narrower terms. The illustration above shows how a search for "facial injuries" includes all terms.