Medical Subject Headings (MeSH®) in MEDLINE®/PubMed®: A Tutorial
Depth of Indexing and the Rule of Three
Rule of Three
- More than 3 major concepts: If more than 3 related topics are each presented as a major topic of the article, the more general MeSH heading under which they are all treed is usually designated as the major topic. The specific headings are usually indexed, but not as major topics.
- More than 3 non-major concepts: If more than 3 related concepts are discussed in an article but are not a major topic, the more general MeSH heading under which they are all treed is usually indexed. The specific headings usually are not indexed.
Note: MeSH Vocabulary present on MEDLINE citations reflect the rules in place at the time of indexing. These rules change over time. This may explain unexpected retrieval in PubMed.