Searching Best Practices for Evidence Synthesis Reviews

Subject headings/controlled vocabulary are standardized terms that are assigned to articles when they are added to a database. This process is called indexing. By using controlled vocabulary, you can find articles on your concept even if the researchers used different terminology to refer to it (heart attack vs. myocardial infarction).

However, the indexing process isn’t perfect. Indexing takes time so brand new articles may not have controlled vocabulary assigned to them yet. Indexing also is a subjective process so the indexer may not include a term that you might use to search for the concept. This is why it is important to also use keywords when searching. Using keywords makes sure that you find any articles that may not have been indexed or may be appropriate despite missing the controlled vocabulary you are using.

Each database has a different controlled vocabulary.

A quality systematic search will include both subject headings and other field codes like title/abstract or text word.

Note: make sure you look up if a database “explodes” their controlled vocabulary automatically. When you search using controlled vocabulary “exploding” the term means that it will search for all the narrower terms under it as well. Some databases do this automatically, like PubMed, and some databases, like Embase, do not. You can tell the database to explode or not explode depending on your search needs, but you need to make sure you know what the default for each database.

Image: If you search for the Mesh Term Anesthesia in PubMed, you will also search all narrower terms in the Mesh hierarchy