Open Access News

News from the open access movement

Wednesday, May 14, 2008

Limiting PMC searches to OA articles

PubMed Central allows users to filter or "limit" searches to OA articles.  To find the option, click the Limits tab on the search page.  (Thanks to Heather Morrison.)

One aspect of this feature seems to be new (more below in the comment), but other aspects are not. 

Here's the part of the Help file on this filter:

Full Text, Free Full Text, and Abstracts

To limit your search results to only citations that include a link to full text, a link to free full text, or an abstract, click the appropriate checkboxes [on the Limits tab].

Alternatively, you may search for citations with links to full text, free full text or include an abstract using the values: full text[sb], free full text[sb], or 'hasabstract'. No search field tag is required for hasabstract.


  • Sometimes when I click on the Limits tab, I see an option labeled "Open Access Articles".  That's what Heather announced and it seems to be new.  At least I haven't seen it before.  But sometimes when I click through, that option is not available, but I see another one to limit searches to "free full text".  That option is not new and I wrote about an earlier version of it in SOAN for August 2005.
  • Unfortunately, once my clicks start to bring up the second option, they no longer bring up the first.  Apart from navigation and interface confusion, this inconsistency raises doubts about the scope of the limited searches.  "Free full text" should include the "public access" articles deposited under the NIH public access policy.  But "Open Access Articles" should not.  The reason is that PMC uses the Bethesda definition of "open access", which calls for the removal of most permission barriers, but the NIH policy does not remove any permission barriers and leaves users with no more than fair use.  It's possible, then, that one of the options covers "public access" papers under the NIH policy and the other one does not.  More later, if I get new clarity on this.

Update.  I just got some clarity from Ed Sequeira at the NLM.  (Thanks, Ed.)  Here's the gist:

  • The PMC (PubMed Central) search page differs from the PM (PubMed) search page.  Each has a Limits tab.  The PMC version shows the "open access" filter and the PM version shows the "free full text" filter.  The clip from the Help file I quoted above is for the PM free full text filter, not for the PMC open access filter.
  • I still don't know how I started on the PMC search page and wound up on the PM search page.  But this may have something to do with it:  the Limits tabs on the two pages have the same URL.  They should display different pages, depending on where you started, and they probably do most of the time.   But in my playing around on Wednesday, it looks like some wires got crossed.
  • The PMC "open access" filter is about a year old.
  • The PMC "open access" filter does not follow the Bethesda definition of "open access", even though that's the definition PMC otherwise endorses.  The filter limits searches to the content in this subset of the larger PMC collection.  (PS:  Some of these articles do, and some don't, live up to the Bethesda definition; all of them are OA due to voluntary publisher policies, not the NIH policy, although some of them are by NIH-funded authors.)