Medical Subject Headings — A Background
The National Library of Medicine (NLM) is the
largest medical library in the world. Its beginnings date to before
the American Civil War. Since 1879, NLM has prepared an index for
articles published in biomedical journals. From that first
manuscript catalog, the service continues into the 21st century in
the form of MEDLINE® and other computer-produced information
databases. Over time, in order to arrange the contents in a useful
way, a controlled vocabulary has been developed for the NLM index.
Beginning in 1960, the Library restructured the vocabulary to
function in a machine-retrieval environment. There are now over 40
years of knowledge available online for analysis by researchers.
MeSH®, the National Library of Medicine's controlled
vocabulary thesaurus, is recognized as the authority for cataloging
and indexing scientific terms. It consists of sets of terms with
descriptors in a hierarchical structure that permits searching at
various levels of specificity. At the most general level of the
hierarchical structure are very broad headings such as "Anatomy" or
"Diseases." At more narrow levels are specific headings such as
"Sternum" and "Scabies." There are approximately 22,000 descriptors
in MeSH®. In addition to these headings, there are over 132,000
headings called Supplementary Concept Records within a separate
chemical thesaurus. There are also thousands of cross-references
that assist in finding the most appropriate MeSH® Heading.
MeSH® is used by NLM for indexing articles from
approximately 4,600 of the world's leading biomedical journals for
the MEDLINE database. It is also used for other NLM-produced
databases that include cataloging of books, documents, and
audiovisuals acquired by the Library. Pharmaceutical companies use
MeSH® for indexing their corporate information. Each bibliographic
reference is associated with a set of MeSH® terms that describe the
content of the item. Similarly, search queries use MeSH® vocabulary
to find items on a desired topic. MeSH® is the source of the
descriptors used in NLM's Index Medicus® and is fundamental to the
organization of this monthly guide to articles from more than 3,700
international journals.
The MeSH® vocabulary is continually revised and
updated by staff experts. New terms are added as they appear in the
scientific literature or in emerging areas of research and are
defined within the context of existing vocabulary.
Indexers must hold an advanced degree in one of the
biomedical sciences and complete an extensive and rigorous training
regimen at NLM facilities in Bethesda, Maryland. Journal assignments
are based on each indexer’s subject and language capabilities and
experience. Stringent deadlines apply, since rapid processing is
required to ensure that citations in MEDLINE® are current.
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