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Expert Searching

Controlled Vocabulary

Controlled vocabularies are a set of predetermined terms that describe specific concepts. You will find that many databases use their own controlled vocabularies (sometimes called index terms, subject headings, or a thesaurus) to enhance the findability of citations. If you have heard of MeSH, this stands for Medical Subject Headings, and is the controlled vocabulary used in PubMed.

Databases that use controlled vocabularies employ subject specialists who review individual citations and add the appropriate controlled vocabulary terms to the citation that describe all of the concepts covered in the article. Using controlled vocabulary terms in your search strategy allows you to locate citations no matter what term(s) an author does or does not use, and helps account for spelling variations and acronyms.

Examples:

 

PubMed's Medical Subject Headings (MeSH): "Renal Insufficiency, Chronic"

 

Embase's Emtree: 'chronic kidney failure'

Keywords

Keywords are the words used in an article title, abstract, or other text field in a database. Keyword searching, or natural language searching, is how most people search for information and is often sufficient for most people. One drawback of searching with keywords is that the words that you use must match the terms used by an author. To remedy this problem, a complete keyword search strategy will include multiple spellings and synonyms that represent the concept. Keyword searching is also useful when attempting to identify literature that may not have been indexed with controlled vocabulary terms, for any variety of reasons.

Example:

chronic kidney disease, chronic renal failure, CKD, CRF

Tips for Selecting Search Terms

Combine Keywords and Controlled Vocabulary Terms

It is good practice to search with both controlled vocabulary and keywords. Here are a few reasons:

  • Not every database uses a controlled vocabulary (Scopus and Web of Science are two examples)
  • Each database has its own controlled vocabulary terms
  • If an article is too new, it may not be indexed with controlled vocabulary yet, and you would only find it with keywords
  • In PubMed, if an article is out of scope of MEDLINE, a component of PubMed, it may not ever be indexed with MeSH (PubMed's controlled vocabulary), and you would only find it with keywords
  • If an article lacks an abstract or additional author-supplied keywords, you may only find it with controlled vocabulary

If you want to be as comprehensive as possible, search with both controlled vocabulary and keywords.


Alternative Method for Finding Controlled Vocabulary Terms

  • Do a basic keyword search and choose a few citations that are relevant to your research question
  • Make a note of any keywords used in the article title or citation you may wish to add to your current list of keywords
  • Examine the full citation information for each article to find the controlled vocabulary terms assigned and write them down
  • Redo your search using both the controlled vocabulary and keyword terms

Avoid Stopwords

In bibliographic databases, stop words are words that the database has been programmed to ignore in a search string or query. Stop words include of, the, is, at, which,and on.

A Key to Database Controlled Vocabulary

 

Database Controlled Vocabulary?
CINAHL Yes, CINAHL Headings
The Cochrane Library Yes, MeSH
Embase Yes, Emtree
ERIC Yes, Thesaurus
Global Health (Ovid) Yes, Thesaurus (part of "Search Tools")
PsycINFO Yes, Thesaurus
PubMed Yes, MeSH
Scopus No
Web of Science No