Medical Subject Headings (MeSH)

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Contents 1 Introduction 1.1 Hierarchical structure 1.2 Explode and focus 1.3 MeSH for indexing 1.4 Subheadings 2 Using MeSH in health-related searching 3 Using MeSH in health libraries 4 Canadian context 5 References

Introduction

See also Medical vocabulary and PubMed - MEDLINE

The Medical Subject Headings - MeSH thesaurus is a controlled vocabulary created by the National Library of Medicine (U.S.). MeSH are used by health librarians to index, catalogue and retrieve biomedical information and documents. The database provides access to ~19 million indexed records from 5,200 worldwide journals in 37 languages; 60 languages for older journals. (See NLM Indexing Process). The 2010 MeSH Database contains 25,186 descriptors or MeSH and Sixteen (16) Major Categories or Trees. Every year, a new MeSH vocabulary is published by the NLM to take account of new concepts in the field of biomedicine. See the Cushing/Whitney Library tutorial and The Basics of MeSH - NLM.

Hierarchical structure

MeSH terms are arranged in a poly-hierarchical tree structure. At the broadest levels, there are categories such as ""Anatomy" or "Organisms"; specific headings at the narrower levels of the sixteen-level hierarchy include "Metatarsal Bones" and "Conduct Disorder." With ~25,186 descriptors and more than 172,000 headings called Supplementary Concept Records, the MeSH vocabulary is one of the largest of its kind in the world. There are thousands of cross-references to assist in locating appropriate terms; Vitamin C, for example, leads searchers to Ascorbic Acid. The explode and focus functions for MeSH help to increase the recall and precision of biomedical searching.

Explode and focus

MEDLINE searchers may use MeSH terms at high levels of generality (mentioned as broadest categories above) or specificity (terms at the bottom of the tree) depending on the goals of the search or literature review. Using the explode function will locate articles indexed with the major descriptor and all specific terms falling underneath it in the hierarchy. Focus locates articles where the term is a major descriptor (not a minor one). Explode and focus can also be used together to locate articles where the major heading and the terms underneath it are the main focus (or descriptors) in the articles retrieved. The entry terms to MeSH descriptors are included in MeSH records and consist of information such as variations in the form, word order, spelling and printed entry term. (There are historic reasons for this which go back to ELHILL days of searching MEDLINE over phone lines). Trade names of drugs and equipment are usually not printed but exist as non-print entry terms. When entry terms are used, PubMed substitutes it with the MeSH descriptor automatically.

MeSH for indexing

The MeSH thesaurus is used by NLM librarians to index articles from ~5,200 international biomedical journals (see Peer review) in the MEDLINE database. Each citation in MEDLINE is given up to fifteen (15) MeSH terms to describe its content. Incidentally, MeSH are also used to provide subject headings for bibliographic records (books, audiovisual materials and digital items) in library catalogues. NLM staff revise and update the MeSH thesaurus annually. Subject librarians are responsible for areas in which they have knowledge and expertise. NLM incorporates new subject headings or terms from the biomedical literature itself and scans emerging areas and new terms regularly. Health professionals in various scientific disciplines are also consulted about any proposed changes to the MeSH vocabulary and there is close coordination with other health organizations who produce specialized vocabularies.

Subheadings

There are 83 floating, allowable subheadings or qualifiers in MEDLINE. These 83 topical qualifiers are used to bring out specific aspects or facets of biomedical topics during the indexing and information retrieval process. Some common subheadings include drug therapy, diagnosis, etiology, surgery, etc. To search for specific subheadings in OvidSP, enter your MeSH term followed by a forward slash and the subheading abbreviation - health care reform/ec for economics of health care reform. Post-coordinate searching is also possible and widely-used by health librarians in systematic review searching. (Certain pre-arranged "Families of Subheadings" can also be searched together and literally exploded.)

Using MeSH in health-related searching

When MeSH terms are not known (or used), health librarians can use textwording and/or keywording. As relevant citations are eventually located, terms associated with these citations can be reviewed and used to rerun a new more structured MeSH-based search. Health librarians constantly restrategize and rerun searches using natural language (See Gault et al) because there may be no relevant MeSH created yet. Keyword searching is a useful way to teach novice searchers or when very current articles are needed. Why? MeSH terms may not yet be created, relevant papers may not yet be indexed or the indexing may not be applied consistently to retrieve everything on a topic.

Using MeSH in health libraries

1. To improve subject use and access in health library OPACs
2. To develop taxonomies for indexing in databases of various kinds
3. To create print and digital pamphlet files
4. To assign key words to journal article submissions by authors
5. To look up definitions in a medical dictionary
6. To assign metadata to digital publications
7. To catalogue items for later search engine retrieval
8. To use in reference interviews to identify concepts and synonyms

Canadian context

Specific issues in Canada's health system are not well-addressed by MeSH due to the American bias in the controlled vocabulary. Geographic subdivisions - Canada, and the provinces - are recommended for issues pertaining to specific regions of Canada ie. HIV infection in the downtown Eastside of Vancouver, try "British Columbia" or "Canada"[MeSH] and "downtown eastside" [keyword].

References

1. The Basics of Medical Subject Headings (MeSH®). NLM, 2009
2. Coletti MH. Medical subject headings used to search the biomedical literature. J Am Med Inform Assoc 2001;8:317-323
3. National Library of Medicine. (MeSH®) Fact Sheet
4. National Library of Medicine. MEDLINE Fact Sheet
5. National Library of Medicine. PubMed's MeSH Database
6. National Library of Medicine. MeSH Browser 2008
7. National Library of Medicine. Bibliography of reference sources used to create MeSH 2008
8. Lipscomb CE. Medical subject headings (MeSH) - 1960-2000. Bull Med Libr Assoc 2000; 88(3): 265-266
9. Understanding Medical Subject Headings (MeSH)
10. NLM Gateway - Unified Interface to NLM
11. NLM's MeSH homepage
12. MeSH Trees - Navigate from Tree Top of Hierarchy
13. MeSH Categories - PubMed
14. Lowe HJ, Barnett GO. Understanding and using the medical subject headings (MeSH) vocabulary to perform literature searches. JAMA 1994;271(14):1103-1108.