When you use no quotation marks, tags, or asterisks, PubMed uses Automatic Term Mapping feature to search for (in this order)
As soon as a match is found, PubMed searching stops. If no match is found, PubMed breaks apart the phrase and repeats the process until a match is found. Phrases and search words are searched in All Fields.
Search hedges are standardized search strings designed to comprehensively search on a concept. Other names are search filters, canned searches, clinical queries, or optimal search strategies. They are specific to a database and are not interchangeable to other databases. They are sometimes published and shared.
Below are some short search hedges for the PubMed database developed by different librarians to find human subjects/patients or to limit to a particular age group. But some can be very long and complex. And notice that there is not only one way to search.
