One of the central tasks undertaken by most faculty and students at a world-class medical center such as CUIMC is researching what others have already done on a given topic and discovering what gaps remain to be explored by further research. Key to this work is searching various databases to understand the literature landscape. When searching for relevant literature, a researcher can use search terms (also known as keywords), controlled vocabulary, or both. This article will discuss when it's most appropriate to use controlled vocabulary and when it’s best to use such vocabulary in conjunction with keywords. We will focus here on PubMed, but the principles hold true across many databases that use controlled vocabulary.
Keywords, which are the terms entered into a search bar, are the most important words or phrases that represent the main concepts of a research question. In contrast to the free-text nature of keywords, controlled vocabulary is a standardized, organized set of terms within a database that describes the content found within that database in a consistent fashion. Many databases have their own unique controlled vocabulary. In the case of PubMed, this is called Medical Subject Headings (MeSH).
Why MeSH terms are helpful
Medical librarian Carrie Price suggests thinking of using a MeSH term like a hashtag on social media, except that a MeSH term is predefined. MeSH terms were created and are updated by the National Library of Medicine (NLM) and each article indexed in PubMed is manually assigned MeSH terms by librarians at the NLM. This manual review provides the benefit of having a professional who has already considered all the synonyms that could be used to describe a particular term and who has read the article and understands its content. Even if the authors of the article have used different keywords or alternative spellings to describe a topic, the article will still appear in the search results when MeSH headings are applied in the search process.
How to find and use a MeSH term
To find a MeSH term of interest in PubMed, first go to the MeSH database. Then search for and select a term of interest.
After the user finds the term they are interested in, they click “Add to search builder” to add the MeSH term to the search box. After they collect and add all the MeSH terms that are useful for the topic, they hit “Search PubMed” to run the search in PubMed, as shown in the upper right corner of the image below.
How to refine a MeSH term search
If this method generates too many results, some of which seem off-topic, here are other ways of focusing the search until the results seem more appropriate:
- Click the “Restrict to MeSH Major Topic” button to only get articles where the MeSH term is one of the main focuses of the piece.
- Click the “Do not include MeSH terms found below this term in the MeSH hierarchy” button to un-explode a MeSH term.
- Check a subheading to get articles that address the MeSH term and that specific subheading.
- Note: Subheadings usually produce very specific results and can be a great starting point for an initial search to explore a topic but are generally best to avoid if the intent is to understand the wider landscape, such as you’d want to do in writing a systematic review, for example.
How to use MeSH terms in a comprehensive search
It is best practice to use both keywords and PubMed’s controlled vocabulary when conducting a comprehensive search for research that will result in a systematic or scoping review. In these cases, instead of using subheadings or restricting the search to the MeSH Major Topic, simply click “Add to search builder” without clicking any additional boxes. Having both MeSH and keywords keeps the search as broad as possible, which helps reduce the possibility of missing relevant articles.
For example, an article relevant to the topic might be tagged with a MeSH term but lacks specific keywords. The same issue could arise where the keyword is present, but the article hasn’t been tagged with the MeSH term. Including keywords is important as MeSH terms are only applied to a specific section of the PubMed collection. Additionally, because of the manual process NLM uses, there is often a 5-month delay for new literature to be fully indexed, so searches that rely only on MeSH terms could miss recent literature (NLM, 2022).
Here’s an example of how to include both MeSH and keywords in a search: “Liver Diseases”[MeSH] OR “liver disease” OR “liver dysfunction”.
Learning how to leverage MeSH terms in PubMed searches will elevate the user’s ability to find relevant articles in a timely manner. We suggest taking some time to experiment with the above techniques.
Citations
Carrie Price. (2022, January 14). PubMed: Find Subject Headings [Video]. YouTube. Retrieved October 18, 2022.
NLM. (2022, January 10). Frequently Asked Questions about Indexing for MEDLINE. Retrieved December 8, 2022.