In PubMed you can use Filters (sometimes referred to as Limits), located on the left hand side of the search results screen to limit your search by certain criteria. The Filters fall into several categories, such as Article Types, Article Language, etc. Some are visible on the search results screen by default, and some can be found and made visible for the future use when clicking Additional Filters button.

The Filters are efficient and handy tools for refining a search, adding desired criteria to your search terms, thus significantly increasing search precision.

However, users may not be aware of the fact that most of the Filters are, in fact, MeSH (Medical Subject Headings) terms set up as clickable Filters but functioning as MeSH terms behind the scenes. For example, if you apply a Clinical Trial Filter, your move will be translated by PubMed as adding a search term “clinical trial”[Publication Type] to your search strategy with an “AND” Boolean Operator, e.g. cancer AND “clinical trial”[Publication Type], Publication Type is a category in the MeSH tree.

Of course, if you are a proficient searcher you can type “clinical trial”[pt], instead of clicking the Filter button which just supports refining your search in an easy and visual way.

Filters are a great feature, however there is a caveat. When you apply a Filter that is a MeSH, your search will automatically be limited to Medline portion of Pubmed. Pubmed is comprised of Medline, as well as many open access articles (mostly coming from Pubmed Central) not indexed for Medline.

To efficiently search Pubmed in it’s entirety, you must construct your search strategy as a combination of MeSH and keywords. MeSH are assigned only to Medline references and there is some lag time in this process. When applying Filters that are based on MeSH to your search it will not retrieve these references only found outside of Medline, as well as some recent Medline references not yet assigned MeSH.

In other words, by using such Filters you limit your search results to Medline only (excluding some very recent references not yet assigned MeSH) instead of getting all Pubmed search results.

The Filter categories that are MeSH terms include:

• Article Type (publication type)
• Species
• Sex
• Age

These filters should be used with caution.

The non-MeSH Filters are safe to use in any search, including:

• Text Availability
• Associated Data
• Publication Date
• Article Language

In conclusion, it is possible to combine applying Filters with using appropriate search terms if you aim at limiting your search by some criteria, yet searching all of PubMed, but as this requires search proficiency it would be best to get assistance at your Library.