Report:MEDLINE/Special Indexing/Keyword or Controlled Vocabulary

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Keyword or Controlled Vocabulary

Medical Subject Headings (MeSH terms) are the controlled vocabulary terms developed for MEDLINE by the National Library of Medicine.

MeSH terms follow a hierarchical structure which begins from broad terms such as "Anatomy" or "Mental Disorders" and narrows in scope across 11 levels of subheadings and 25,186 total descriptors.[1]

In addition to this hierarchy of subheadings, there is a separate thesaurus of more than 180,000 "Supplementary Concept Records" (also may be referred to by the former title of Supplementary Chemical Records within some hosts). These supplemental concept records are edited and added daily, and include the following types of tags:[2]

  • name of substance
  • synonyms
  • CAS type 1 name
  • CAS registry/ec name and number
  • related CAS registry number
  • heading mapped to
  • indexing information
  • note
  • pharmacological action
  • previous indexing


To access and browse a MeSH term thesaurus, users can utilize search engine tools such as those found in PubMed, EBSCOhost, Dialog, or STN; alternatively, users may refer directly to the MeSH homepage. This homepage offers free MeSH definitions and explanations, links to online searching, change logs, help sheets, and frequently asked questions.


The MeSH homepage offers many ways to learn about the MeSH classification system


One notable feature of searching using MeSH terms is that users are able to search the MeSH thesaurus using related terms called "entry terms". For example,when users enter "Vitamin C", they will be directed to the "Ascorbic Acid" MeSH entry.[3]

The MeSH term thesaurus is updated and maintained by a staff of 11 subject area experts, and a new edition of MeSH terms coincides with the yearly re-load of the file. The new edition of MeSH terms are not usually retroactively applied to the existing database, although there are some exceptions. According to the National Library of Medicine: " Typically, NLM does not retrospectively re-index MEDLINE records with new MeSH Heading concepts. Therefore, searching for a new MeSH term tagged with [mh] or [majr] effectively limits retrieval to records indexed after the term was introduced."[4] To compensate for the fact that MeSH terms are time dependent, users can search the MeSH database for likely "Previous Indexing Terms" that suggest related terms used prior to a specific term's introduction.

One exception occurs when an out-of-date term is replaced with a currently used or more accurate term. When this change takes place in the MeSH term Thesaurus, records tagged with the old term will be replaced with the new term's tag, and the old term will remain as an "entry term". Entry terms map to and direct users to the new term when searched.


Sources

  1. "Medical Subject Headings Fact Sheet." National Library of Medicine website, http://www.nlm.nih.gov/pubs/factsheets/mesh.html. Accessed on January 16, 2009.
  2. "Relationships in Medical Subject Headings." NLM website, http://www.nlm.nih.gov/mesh/meshrels.html. Accessed on January 22, 2009.
  3. "Medical Subject Headings Fact Sheet." National Library of Medicine website, http://www.nlm.nih.gov/pubs/factsheets/mesh.html. Accessed on January 16, 2009.
  4. "MEDLINE Data Changes - 2009." National Library of Medicine website, http://www.nlm.nih.gov/pubs/techbull/nd08/nd08_medline_data_changes_2009.html. Accessed on January 16, 2009.
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