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University of Wollongong Australia

Systematic Review

How the Library can help when you're conducting a systematic review

Controlled Vocabularies 

A controlled vocabulary is an organised set of phrases or words used to index content in a database so that it can be efficiently retrieved. These are sometimes referred to as subject terms, subject headings, thesaurus terms, or index terms. Examples of controlled vocabularies include Medical Subject Headings (MeSH), APA Thesaurus of Psychological Index Terms and CINAHL Subject Headings. 

Not every database uses a controlled vocabulary. They are typically only used in disciplines where the subject matter is so complex that it would be impossible to retrieve all relevant articles using keywords alone. The controlled vocabulary provides a way of structuring the subject matter to create consistency (e.g., searching for Dysphoria, Melancholia, and Depression can all be achieved by searching the term “Major Depression”).

If the database uses a controlled vocabulary, the articles in it are assessed by reviewers, who assign the appropriate term/s to the article. Each term will have a scope note so you can make sure it is appropriate for your particular topic. For example, from MeSH: 

  • “Working dogs” - Dogs that are trained to perform practical tasks, as opposed to PETS or companion dogs.

  • “Dogs”  - The domestic dog, Canis familiaris, comprising about 400 breeds, of the carnivore family CANIDAE.

Searching both controlled vocabulary and keywords 

It is important to note that not every article will be assigned a term from a database's controlled vocabulary. For example, the article may be so new to the database that it has not yet been assessed. For this reason, always search subject terms as well as keywords for the most thorough search – especially if you are doing a systematic review. For example:  

  • "Dogs"[MeSH] OR dog* 

This search query will bring back citations with the MeSH term dogs, as well as any citations where dogs are mentioned in the title, abstract, or authors fields as a keyword term. 

How to use MeSH  

This video shows an example of working with a controlled vocabulary. The principles shown here, using MeSH, apply to other controlled vocabularies, though the terms may be different.

Controlled vocabularies in UOW Databases 

Below is a list of UOW databases with the controlled vocabulary they use.  

  • MEDLINE: Medical Subject Headings (MeSH) - tutorial 
  • PubMed: Medical Subject Headings (MeSH) - tutorial 
  • Cochrane: Medical Subject Headings (MeSH) - tutorial 
  • CINAHL: CINAHL Subject Headings – tutorial  
  • PsycINFO: APA Thesaurus of Psychological Index Terms - tutorial
  • IEEE Xplore: IEEE Thesaurus - tutorial

Evaluate your use of controlled vocabularies

When using controlled vocabularies, consider: 

  • Are the subject headings relevant? 
  • Are any relevant subject headings missing; for example, previous index terms? 
  • Are any subject headings too broad or too narrow? 
  • Are subject headings exploded where necessary and vice versa? 
  • Are major headings (“starring” or restrict to focus) used? If so, is there adequate justification? 
  • Are subheadings missing? 
  • Are both subject headings and keyword search used for each concept? 

Adapted from McGowan, J., Sampson, M., Salzwedel, D.M., Cogo, E., Foerster, V. and Lefebvre, C., 2016. PRESS peer review of electronic search strategies: 2015 guideline statementJournal of clinical epidemiology75, pp.40-46.