Note: This is an abbreviated version of the article provided by the authors; the full-text is available online or by contacting PSRML.
In brief, this article discusses two of PubMed's indexes, the All Fields index and the MeSH Terms index, and how the search rules used to create these indexes affect your retrieval. MeSH terms are treated differently in these two indexes.
The All Fields index does not include MeSH entry terms and the MeSH terms are NOT exploded; every MeSH term listed includes all postings (main point of article or not, attached subheading or not).
The MeSH Terms index does not include MeSH entry terms, but the MeSH terms ARE exploded; every MeSH term listed includes all postings (main point of article or not, attached subheading or not).
MeSH Entry terms work through one of several Translation Tables that PubMed invokes for all unqualified (and also MH qualified) search terms.
Truncation of unqualified terms bypasses all Translation Tables and directly looks in the All Fields index for a match; therefore, truncation "turns off" automatic MeSH mapping and explosions.
Truncation incorporates the first 150 variations of the root term in the search and gives a warning message. For comprehensive results the search may need to be redone using a longer root term(s).
Use the List Terms Mode with caution remembering the differences in the way the All Fields and MeSH Terms indexes are built and realizing that the entry terms do not post in the indexes.