Focused Searches

Knowledge Discovery with MeSH (Explode & Focus) – Ovid MEDLINE

How to instruct the database to include narrower terms in a MeSH thesaurus search and/or to retrieve only those terms considered main subject terms.

Ovid MEDLINE

Ovid Training Team

2024-10-27

77 visits

Background

This Focused Search provides further background on the structure and system of the MeSH thesaurus. The MeSH thesaurus is a controlled vocabulary, based upon medical subject headings. It has been created and is maintained by the National Library of Medicine (NLM) in the USA. The MeSH thesaurus is a domain specific knowledge base curated by humans, that aids both document classification as well as discoverability and retrieval.

MeSH Structure and System
Ovid MEDLINE is Ovid’s rendering of the PubMed database, it too created and maintained by NLM. The content of this kind of bibliographic database consists, for the most part, of records of documents that have been indexed using a controlled vocabulary. A controlled vocabulary is a hierarchical term classification system where terms, representing a thing or concept, can be located within the controlled vocabulary system, along with its broader and narrower terms. Broader terms are those for which your chosen term is a narrower term or sub-concept. Narrower terms on the other hand are the narrower terms or sub-concepts of your chosen term.

Using MeSH for Targeted Searching
We have already seen how, on Ovid, you can use the Advanced Search search mode to locate a term in a specific field (i.e. migraine.ti., see line #1 in this Focused Search) or in a group of fields (i.e. migraine.mp., see line #2).

In the Advanced Search, with mapping turned on (which for most users is a default setting) you can search for a thing not just in terms of the characters that describe it i.e. ‘migraine’, but also in a conceptual sense. That is you are able to automatically include additional terms and phrases that more fully represent the concept that best describes the thing you are looking for. In this Focused Search the entry term for all 10 search lines, using the Advanced Search with mapping turned on, is migraine. With mapping turned on, our search journey starts and continues through the MeSH thesaurus where at various stages we are offered opportunities to expand upon or narrow the scope of our search (see lines #3 to #10).

To investigate this further, let’s consider the following research question and subsequent task.

Is acupuncture effective in the treatment of migraines? Find randomised controlled trials.

From the research question, let us describe the population group as ‘migraine sufferers’ and that by proceeding with the search term ‘migraine’ we are likely to capture a relatively high proportion of relevant documents.

Upon entering the term migraine into the Advanced Search search mode with mapping turned on, Ovid maps our entered term onto a MeSH term, in this case Migraine Disorders/ (see line #3).  Clicking on the MeSH terms displays it in the context of its occurrence and positioning within the controlled vocabulary  as displayed below. Here we can see that Migraine Disorders is a sub-term of the broader term, Headache Disorders, Primary. But Migraine Disorders is itself the broader term for its narrower terms, namely Alice in Wonderland Syndrome, Migraine with Aura, Migraine without Aura and Ophthalmoplegic Migraine.

A screenshot of a computer

Description automatically generated

The returned display, which highlights the mapped to term Migraine Disorders/, also tells us that a specific number of documents, indicated by the search results have been indexed with that specific term. In other words, the concept or idea represented by the term ‘migraine’ within a constellation of scope defining broader and narrower terms, has been identified in the database. This, as opposed to ‘just’ occurrences of the word ‘migraine’ as is the case in lines #1 and #2.

Explode and Focus Options
The MeSH thesaurus, both in terms of its structure and direct integration in Ovid MEDLINE, also facilitates systematic searching. The scope of a selected MeSH term can be expanded upon by selecting the Explode option next to the selected term. See the green highlighting in the screen shot above. MeSH terms displayed in a search strategy with the ‘exp’, as shown in line #5 of the displayed Focused Search, tells us that the total number of records returned for that search line includes the MeSH term along with its narrower terms. By contrast, selecting the Focus option, highlighted in purple above, reduces the scope of the term, whether exploded or not, to records where the selected MeSH term represents one of the main topics as described in the article. The ‘*’ character placed before the MeSH term, as displayed in line #4 , indicates that the search has been run with this more specific requirement in mind. 

MeSH Subheadings
Each MeSH term has a collection of subheadings associated with it. The list of subheadings for the MeSH term Migraine Disorders is displayed in the screen shot below.

A screenshot of a medical survey

Description automatically generated

As part of MeSH thesaurus construction and maintenance, the indexers at NLM allocate subheadings to MeSH terms. Subheadings provide an additional means of further fine-tuning the context within which the MeSH term, i.e. the concept, is being sought. In the displayed Focused Search, lines #6, #7 and #8 return records that cover Migraine Disorders but specifically those related to the etiology, diagnosis and prevention and control of the condition respectively. It is also possible to select multiple subheadings as shown with respect to therapy, in line #9. 

Practice Suggestions

  1. Does the subheading /dh – Diet Therapy include vitamin or mineral supplements? Use the ‘i’ icon next to the subheading to find out.   
  2. How many PubMed-not-MEDLINE records would you expect to find in line #5 of the displayed Focused Search? Look at the Focused Search, Database Size and Shape (docz.dz) – Ovid MEDLINE to help you find the answer.
  3. Describe what Ovid is doing in line #10 of the displayed Focused Search. In terms of database record status, what type or types of database record are being returned with this search? Would this search also run in Embase on Ovid although it has been formulated using MeSH terms?

 

Search Stategy

migraine.ti.

migraine.mp.

Migraine Disorders/

*Migraine Disorders/

exp Migraine Disorders/             

exp Migraine Disorders/et [Etiology]

exp Migraine Disorders/di [Diagnosis]

exp Migraine Disorders/pc [Prevention & Control]

exp Migraine Disorders/dh, dt, th [Diet Therapy, Drug Therapy, Therapy]           

exp Migraine Disorders/ or migraine.mp.

 

Launch Search

Reviewers

Primary: Michael Fanning

Secondary: Charlotte Viken

Review Date: 2024-10-27

Expiry Date: 2025-10-27

Original search produced by:

Ovid Training Team

Citation:

OvidGO! Portal. Focused Searches: Knowledge Discovery with MeSH (Explode & Focus) – Ovid MEDLINE [Internet]. London (UK): Ovid Training Team (Editors); 2024 [updated 25 October 2024; cited 30 October 2024]. Available from: https://tools.ovid.com/ovidgo/searches/view.php?id=58