MEDICAL SUBJECT HEADINGS (MeSH®)

The Thesaurus

MeSH is the National Library of Medicine's controlled vocabulary thesaurus. Thesauri are carefully constructed sets of terms often connected by "broader-than," narrower-than," and "related" links. Synonyms for the term thesaurus are "classification structure," "controlled vocabulary," and "ordering system." A well-constructed thesaurus links related terms and provides a hierarchical structure that permits generic searches to be conducted.

MeSH consists of a set of terms or subject headings arranged in both an alphabetic and a hierarchical structure. At the most general level of the hierarchical structure, headings include, for example, "anatomical terms," "diseases," and "chemicals and drugs." At the more detailed level are names of specific neoplastic, immunologic, and viral diseases. There are more than 16,000 main headings in the primary structure of MeSH. In addition to these main headings, there are an additional 59,000 headings within a special chemical thesaurus. Thousands of cross-references assist the user in finding the appropriate MeSH heading.

MeSH Applications

The quality of an information retrieval system is determined in large part by the effectiveness of the selection and assignment of thesaurus terms to documents represented in the system so that searchers may easily retrieve pertinent documents. MeSH, one of the world's preeminent controlled vocabularies, is a vital part of the Library's computer-based Medical Literature Analysis and Retrieval System (MEDLARS®).
The MeSH thesaurus is used by NLM for indexing articles from more than 3,900 of the world's leading biomedical journals and for cataloging books, documents, and audiovisuals acquired by the Library. Each bibliographic reference to a document is associated with a set of MeSH terms that describe the con-tent of the document. A retrieval query can also be represented by a set of MeSH terms.
MeSH is the source of the subject headings for NLM's Index Medicus® and is fundamental to the organization of this monthly subject/author guide to articles in nearly 3,000 journals.

Establishing and Updating MeSH

The staff of the Medical Subject Headings Section are continually revising and updating the MeSH vocabulary. Subject specialists are responsible for areas of the health sciences in which they have knowledge and experience. In addition to receiving suggestions from indexers and others, the specialists collect new terms as they appear in the scientific literature or in emerging areas of research, define them, establish their relationships with other terms in the vocabulary, and recommend their addition to MeSH. A term is either accepted or rejected as a usable concept after the recommendation has been reviewed and commented upon by senior indexers, searchers, catalogers, and reference staff. The MeSH staff frequently discuss terminology with scientists working in the biomedical disciplines who provide the additional specialized knowledge required to keep the vocabulary current with progress being made in science.

MeSH Publications

MeSH, in machine-readable form, is provided free to those who license MEDLINE® and is also available separately. It is also published in several printed forms. The headings used in Index Medicus are published in January as a supplement to Index Medicus and are included in Cumulated Index Medicus. These headings appear both alphabetically and hierarchically ordered in the two publications. More exhaustive descriptions of MeSH can be obtained from:

MeSH - Annotated Alphabetic List,
MeSH - Tree Structures,
Permuted MeSH, and
MeSH - Supplementary Chemical Records.

In the Annotated Alphabetic List, many headings are accompanied by notes for indexers, catalogers, and searchers, as well as historical information for assistance in searching the earlier online files. The MeSH Tree Structures presents the hierarchical ordering of MeSH. The Permuted MeSH consists of a listing of each significant word or root that appears in any MeSH heading. The MeSH Supplementary Chemical Records contains records of about 22,000 chemicals which have proved to be significant in journals indexed in MEDLINE. The supplementary chemical terms can be directly used by indexers and online searchers.

Questions about the Library's MeSH program may be directed to:

Head
Medical Subject Headings
National Library of Medicine
8600 Rockville Pike
Bethesda, MD 20894
(301) 496-1495

NLM HyperDOC / Medical Subject Headings (MeSH) / January 1993