Table 1.

Some operators used in PubMed

Operator	Meaning
[ti]	The term is considered as a free text keyword and searched for in title
[ab]	The term is considered as a free text keyword and searched for in abstract
[mh]	The term, a MeSH descriptor, and all the terms it subsumes, are searched for in MeSH indexing
[majr]	The term, a MeSH descriptor, and all the terms it subsumes, are searched for in MeSH major indexing
[nm]	The term, a MeSH supplementary concept, is searched for in MeSH indexing
[tw]	The term is considered as a free text keyword and searched for in multiple fields of PubMed citation (title, abstract, MeSH indexing, other keywords etc.)