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Medical Subject Headings

History of MeSH

The first official list of subject headings published by theNational Library of Medicine appeared in 1954 under the titleSubject Heading Authority List. It was based on theinternal authority list that had been used for publication ofCurrent List of Medical Literature which in turn hadincorporated headings from the Library's Index-Catalogueand from the 1940 Quarterly Cumulative Index MedicusSubject Headings. With the inception of Index Medicus in1960, a new and thoroughly revised Medical Subject Headingsappeared.

With the 1954 Subject Heading Authority List, there appeared a"Categorical Listing" of standard subheadings. "Abnormalities,"for instance, was listed as a standard subheading for use withterms for organs, tissues, and regions, and "anesthesia andanalgesia" was to be used under surgical procedure headings. Butsuch subheadings could be used only for subject headings whichfell within the category of headings to which they were to beapplied. There were over 100 such subheadings, some of whichvaried only slightly according to the category of main headingwith which they were used. For instance, "therapeutic use" wasused under physical agents and drugs and chemicals, and "therapy"was used with diseases. In the 1960 Medical Subject Headings, thenumber of subheadings was reduced to sixty-seven. They could beused under any kind of main heading if the combination was notpatently foolish or impossible. These sixty-seven subheadingswere applied with more generalized meanings. For instance, thesubheading "therapy" was used to mean "therapy of," "therapeuticuse of" or just "therapeutic aspects." Though this solution wassimpler, many problems still remained. The use of one subheadingmight prevent the use of another. For instance, if a papercovered the etiology, pathology, and therapy of a disease, itmight occur without further subdivision, or it might occur underthe subheading which seemed most appropriate to the indexer. If"therapy" was chosen, the article would be lost to the searcherlooking for the etiology of the disease under the subheading"etiology." In addition, if the subheading "diseases" had beenappended to the term for an anatomic part, it would not bepossible to subdivide further for the therapy or complications ofsuch diseases. A related problem was the overlap in meaning ofthe subheadings themselves. It was difficult, for example, todecide whether a paper on chemical biosynthesis fit best under"chemistry" or "metabolism."

Categorized lists of terms were printed for the first time inthe 1963 Medical Subject Headings and contained thirteenmain categories and a total of fifty-eight separate groups insubcategories and main categories. These categorized lists madeit possible for the user to find many more related terms thanwere in the former cross-reference structure. In 1963, the secondedition of Medical Subject Headings contained 5,700descriptors, compared with 4,400 in the 1960 edition. Of theheadings used in the 1960 list, 113 were withdrawn in favor ofnewer terms. In contrast, the 2005 edition of MeSH contains22,995 descriptors.

In 1960, medical librarianship was on the cusp of arevolution. The first issue of the new Index Medicusseries was published. On the horizon was a computerizationproject undertaken by the National Library of Medicine (NLM) tostore and retrieve information. The Medical Literature Analysisand Retrieval System (MEDLARS) would speed the publicationprocess for bibliographies such as Index Medicus,facilitate the expansion of coverage of the literature, andpermit searches for individuals upon demand. The new list ofsubject headings introduced in 1960 was the underpinning of theanalysis and retrieval operation. MeSH was a new and thoroughlyrevised version of lists of subject headings compiled by NLM forits bibliographies and cataloging. Frank B. Rogers, then NLMdirector, announced several innovations as he introduced MeSH in1960.

The adoption of a single subject authority list for bothbooks and periodical articles is a departure from traditionalpractice. We take the view that subject cataloging and periodicalindexing, as exemplified in the Index Medicus and in the NLMCatalog, are identical processes in their major dimensions. Asingle list can and should be used for both purposes. This hastwo major virtues: simplicity for users, in requiring familiaritywith only a single scheme; and economy to the Library in thedevelopment and maintenance of a single scheme.

There is another departure from traditional practicerepresented in this list. This is the adoption of standardtopical subheadings for cataloging books, as well as for indexingperiodical articles. The topical subheading is in effect asubstitute for a phrase heading, and on the whole it is apreferable substitute.

The main heading-topical subheading combination is apre-coordination of terms, reducing the problem of termpermutation, which looms large in most manual retrieval systemsin book form.

From its beginning, MeSH was intended to be a dynamic list,with procedures for recommending and examining the need for newheadings. The content of the vocabulary related to the usage ofterms in the literature itself and evolved to meet new conceptsin the field. The use of the computer made revisions morepractical and systematic, despite the difficulty in updatingprinted indexes and card catalogs.