MEDLINE allows users to expand a category of terms from the MeSH TREES (MeSH terms in a hierarchy from general to specific) to retrieve all of the articles on the general term and all of the specific terms listed underneath. Terms are automatically expanded in PubMed unless you change the default. For Example:
'Cohort Studies' would include: 'Longitudinal Studies', 'Follow-up Studies', and 'Prospective Studies'
'Longitudinal Studies' would include: 'Follow-up Studies' and 'Prospective Studies'
Subheadings are terms which cover general, frequently discussed aspects of a subject (e.g. diagnosis, etiology, surgery, therapy). Subheadings are combined with MeSH terms to indicate a specific focus. (Example: ASPIRIN/adverse effects)
Understanding Publication Types versus MeSH Terms:
Publication Type [PT] is always singular (Practice Guideline) while MeSH terms are always plural (Practice Guidelines). [PT] indicates the report in the article is a Practice Guideline. An article which has been indexed with the MeSH term Practice Guidelines is an article about this methodology or process. Some searchers, in order to be as comprehensive as possible, will use the strategy: Practice Guideline [PT] OR Practice Guidelines [MeSH].