4. Expand a PubMed search with too few results

Sometimes, there are few or no results at all. In these cases, neither descriptors nor filters should be used.

Remember that these descriptors are qualified by human beings, librarians at the NLM (United States National Library of Medicine). An article analysis takes time, and there is a delay before the keywords are finally indexed.

In Medline, articles are indexed according to three categories:

• PubMed – indexed for Medline ;

• PubMed – in process: indicates that the Medline team is in the process of collecting descriptors;

• PubMed – as supplied by publisher: indicates that indexing has been done on the basis of keywords supplied with the article, but not yet described according to MeSH terms.

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