Medical Subject Headings
MeSH Record Types
The following is a list of the three basic types of MeSH Records: Descriptors, Qualifiers, and Supplementary Concept Records (SCRs)
This record type plays a central role in MeSH vocabulary as a unit of Indexing and retrieval. With the exception of Class 3 Descriptors, all descriptors are organised into a numbered tree structure or hierarchy that allows users to browse in a orderly fashion from broader to narrower topics. Descriptors are divided into four classes.
- Class 1 Descriptors - Main Headings
- These records are topical headings that are used to index citations in NLM's MEDLINE database, for cataloging of publications, and other databases, and are searchable in PubMed as [MH]. Most Descriptors indicate the subject of an indexed item, such as a journal article, that is, what the article is about. Descriptors are generally updated on an annual basis but may, on occasion, be updated more frequently.
- Class 2 Descriptors - Publication Characteristics (Publication Types)
- These records indicate what the indexed item is, i.e., its genre, rather than what it is about, for example, Historical Article. They may include Publication Components, such as Charts; Publication Formats, such as Editorial; and Study Characteristics, such as Clinical Trial. They function as metadata, rather than being about the content. These records are searchable in PubMed as Publication Type [PT], and the terms in MEDLINE records are labeled as "PT" or <PublicationType> rather than "MH" or <MeSHHeading>. They are listed in category V of the MeSH Tree Structures. A list is available of Publication Types, with Scope Notes.
- Class 3 Descriptors - Check Tags
- This class of descriptors is used solely for tagging citations that contain certain categories of information. They do not appear in the MeSH tree. Modernization has largely eliminated the need for the data type and many of the Check Tags have been changed to Class 1 headings that can be used either a MH or a Check Tag. Currently only two Class 3 descriptors remain: "Male" and "Female".
- Class 4 Descriptors - Geographics
- Descriptors which include continents, regions, countries, states, and other geographic subdivisions. They are not used to characterize subject content but rather physical location. They are listed in category Z of the MeSH Tree Structures.
There are 82 topical Qualifiers (also known as Subheadings) used for indexing and cataloging in conjunction with Descriptors. Qualifiers afford a convenient means of grouping together those citations which are concerned with a particular aspect of a subject. For example, Liver/drug effects indicates that the article or book is not about the liver in general, but about the effect of drugs on the liver Qualifiers are searchable in PubMed as MeSH Subheadings [SH]. There is only a single type of Qualifiers in MeSH. The qualifers are listed below.
- Qualifiers, with Scope Notes
- Qualifiers by Allowable Category (also known as AQ Lists)
- Qualifier Tree Hierarchy
Supplementary Records, also called Supplementary Chemical Records(SCRs), are used to index chemicals, drugs, and other concepts such as rare diseases for MEDLINE and are searchable by Substance Name [NM] in PubMed. Unlike Descriptors, SCRs are not organised in a tree hierarchy. Instead each SCR is linked to one or more Descriptors by the Heading Mapped To (HM) field in the SCR. They also include a Indexing Information (II) field field that is used to refer to other descriptors that are from related topics. SCRs are created daily and distributed nightly Monday-Thursday. There are currently over 230,000 SCR records with over 505,000 SCR terms. Like all MeSH records, SCRs are searchable in the MeSH Browser. Three classes of SCRs exist.
- Class 1 Supplementary Records
- These records are dedicated to chemicals and are primarily heading mapped to the D tree descriptors.
- Class 2 Supplementary Records
- These records are dedicated to Chemotherapy Protocols. They are heading mapped to the MeSH heading "Antineoplastic Combined Chemotherapy Protocols" and to chemicals used in the protocols found in D tree descriptors.
- Class 3 Supplementary Records
- These records are dedicated to diseases and are primarily heading mapped to the C tree descriptors and anatomical headings found in the A tree.
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