Controlled vocabulary
Controlled vocabulary
Many reference databases use controlled search keywords to index articles. These controlled search keywords typically describe all or parts of the content of each article. Therefore, controlled search keywords can be used to yield precise results in relevant references when conducting a literature search. Controlled search keywords can be found by searching in the controlled vocabulary of each database. The databases that use controlled vocabulary often use terms like subject headings, subject terms, index terms, or descriptors to describe the controlled search keywords. The controlled search keywords may vary between the different controlled vocabularies used in the various databases. Therefore, you must be careful to look up the controlled search keywords again when you change the database you are searching in!
You can find examples of controlled vocabularies in databases available via the University Library at UiT:
- MeSH - Medical Subject Headings (PubMed, Medline via Ovid, Cochrane)
- Emtree (Embase via Ovid)
- CINAHL Subject Headings (CINAHL via EBSCO)
- Thesaurus of Psychological Index Terms (PsycINFO via Ovid)
It is very useful to include controlled search keywords in your literature searches. Controlled search keywords will return references where different or synonymous words are used for the main element you are searching for. Controlled search keywords will also retrieve references where elements of interest are not necessarily expressed in the title or abstract.
Note: You must always try to find controlled search keywords for each of your main elements in the search setup. This must be done in the controlled vocabulary of the specific database in which you wish to conduct a literature search. This must be done for each database you search in, as the controlled search keywords may differ in the various databases.
Example: Controlled search keywords in different databases
We want to find a controlled search keyword in Ovid Medline for trauma caused by external force. By searching in Medline's MeSH vocabulary for the word 'Trauma', we find that Medline's controlled search keyword ('Subject Heading') for 'Trauma' is: 'Wounds and Injuries'.
If we repeat this search for the controlled search keyword for 'Trauma' in Ovid Embase's Emtree vocabulary, we find that Embase's controlled search keyword ('Subject Heading') for 'Trauma' is: 'Injury'.
Explode / Not Explode
The controlled vocabulary of individual databases is set up in a hierarchical structure. This means that the further down you move in the hierarchy, the more precise the search result becomes. It is very important that you ALWAYS read the explanation ('Scope Note') for the controlled search keyword you want to use. Since the databases' controlled vocabulary is built up in a hierarchical structure, you must choose whether to:
- Use ONLY the exact controlled search keyword ('Subject Heading'). That is: 'Not Explode'. Then you do not include the underlying, more specific terms in the hierarchical structure.
- Include all the more specific underlying terms in the hierarchical structure. That is: 'Explode'.
- "Pick and choose" from different levels in the hierarchical structure, so that you cover what your main element requires.
As a rule, the most broadly defined controlled search keyword from your main concept should be used.
Whether the controlled search keyword is automatically exploded or not varies from database to database.
- PubMed: preset 'Explode'
- Ovid databases (Medline, Embase, PsycINFO): preset 'Not Explode'
- CINAHL: preset 'Not Explode'
Example from Ovid Medline
We want to find a controlled search keyword for our main concept: Cancer in the mammary gland in women. However, we are unsure what the controlled search keyword is, but know it must be related to cancer.
Therefore, we search for the word 'Cancer' in Medline's 'Advanced' search interface:
We then get the following suggestion for a controlled search keyword ('Subject Heading') in Medline's controlled vocabulary (MeSH): 'Neoplasms'. This is the scientific term for cancer.
By clicking on 'Neoplasms', we get the hierarchical structure of the controlled search keyword, 'Neoplasms'.
Here we see that under the overarching search keyword 'Neoplasms' there are several more specific terms for cancer. Some of these have even more specific search keywords under them, which we can choose to investigate by clicking on the + sign in front of each controlled search keyword.
We want to find a controlled search keyword for 'cancer in the mammary gland in women', so we therefore click on the + sign to the left of 'Neoplasms by Site'.
We then see that under 'Neoplasms by Site' there is a level called 'Breast Neoplasms'. We therefore click on the + sign in front of 'Breast Neoplasms' and get a more specific overview of the various types of cancer that are included under this level in the hierarchical structure.
By clicking 'Scope Note' for each of these underlying terms, we find that 'Carcinoma, Lobular' is the term we are looking for in relation to our main concept, ‘cancer in the mammary gland in women'.
Now it's up to you as a student/researcher, which level in this structure you want to conduct your search on. If you trust that those who index the articles in this database have done a flawless job, you choose only the level for 'Carcinoma, Lobular', which will give you 6169 references.
If you think that those who index the articles in this database are probably not medical clinicians, you should also include the level above 'Carcinoma, Lobular' (recommended).
If you think that all articles under 'Breast Neoplasms' will be interesting to include as one of several main concepts, you should check off for 'Explode'.
This will include all articles that are indexed to deal with 'Breast Neoplasms' and the more specific terms under this level in the hierarchical structure.
