Standardized terminology applied by indexers to records in a database. Each database has its own unique terminology that best represents the subject areas covered. Indexers assign the most specific terms available. Use of controlled vocabulary as search terms improves consistency, recall, and precision. Example: PubMed's controlled vocabulary is collected in the Medical Subject Headings (MeSH).
User-selected terms which can be single terms or phrases. The use of these terms results in a search of the entire citation (e.g. title, abstract, index terms), but these terms may or may not reflect an article's key concepts. The use of natural language terms finds a high proportion of relevant articles (to maximize recall) and captures the most recent citations. They include all known synonyms and variations in usage (spelling, plurals, etc.). Tip: Suggestions for keyword terms are often listed in controlled vocabulary records in the "entry terms" or "synonyms" sections.
The proportion of relevant documents that are retrieved. (Van Rijsbergen, 1979, p.6)
The proportion of retrieved documents that are relevant. (Van Rijsbergen, 1979, p.6). This is determined by the number of relevant reports identified divided by the total number of reports identified. (Cochrane Handbook, Part 2, 6.4.4, Higgins & Green, eds, 2011)
A unique numeric identifier assigned to documents in PubMed.