Principles of MEDLINE Subject Indexing

The types of vocabulary terms are:

• MeSH headings ("descriptors")
• Subheadings ("qualifiers")
• Check tags 
  • A special class of MeSH headings that must be considered routinely for every article
    • Primarily headings covering species (including Humans), sex, and human age groups
    • Also cover:
      • historical time periods
      • pregnancy
  • Usually are indexed even if merely mentioned, unlike other MeSH headings
  • For review articles, usually are indexed only if the main point of the article
  • Humans is not selected for articles involving institutions that serve humans, e.g., clinics, hospitals
  • Some check tags (e.g., Animals, Humans, Male, Female) can never be designated as the main point of the article
• Publication Characteristics (or Types): describe the item being indexed rather than its topic.   There are 3 main categories:
  • Publication Components, e.g., English Abstract
  • Publication Formats, e.g., Lectures, Letter
  • Study Characteristics, e.g., Clinical Trial, Twin Study
• Supplementary Concept Records: allow the indexing and searching of non-MeSH headings, primarily substances but also some protocols, some virus terms and rare disease terms.