Definition of Structured Abstracts Expanded to Enhance Readability

In 2010, structured abstracts in PubMed were reformatted for easier readability with bolded, uppercase section labels followed by a colon beginning on a new line. NLM previously defined a Structured Abstract to be:

". . . one that contained at least 3 labels that represented 3 distinct concepts (e.g., "INTRODUCTION," "METHODS," "CONCLUSIONS"), of which 1 must be considered an ending concept (such as "RESULTS" or "CONCLUSIONS").

To enhance readability, NLM's new definition of Structured Abstracts is:

...one that has at least one label that:

• is listed on the (8/31/12) Updated Label List and NLM Category Mappings; or
• is electronically submitted by publishers as part of supplied citations’ abstracts; or
• is identified by NLM PubMed data import procedures.

To accommodate this broadened definition, NLM made a mid-year 2013 change to the NLMMedlineCitationSet DTD (used for MEDLINE/PubMed processing) which added a new NlmCategory attribute valid value, UNASSIGNED. The UNASSIGNED NlmCategory is used for labels in structured abstracts that NLM has not yet mapped to one of five categories, i.e., BACKGROUND, OBJECTIVE, METHODS, RESULTS, CONCLUSIONS.

Prior to expanding the definition of structured abstracts to include abstracts that contain fewer than three labels and adding the UNASSIGNED valid value, the display of these abstracts remained in a single paragraph format (see Figure 1).

Figure 1: Abstract in single paragraph format but with two labels.

After expanding the definition of structured abstracts to include abstracts that contain fewer than three labels and UNASSIGNED mapping, these abstracts are also reformatted for easier readability. Section labels remain in uppercase followed by a colon, and are bolded with each section beginning on a new line (see Figure 2).

Figure 2: Reformatted PubMed Structured Abstract having fewer than three labels.

These PubMed structured abstracts having fewer than three labels will be added to the PubMed search feature that allows for a search of structured abstracts. [Editor’s Note: The following sentence was changed on July 18, 2013.] Effective June 21, 2013, citations with the status of publisher, i.e., publisher[sb], that have structured abstracts are also included in these search results.

Researchers or licensees who wish to continue using the stricter definition of structured abstracts may do so. The Structured Abstracts in MEDLINE Web site continues to have the Updated Label List and NLM Category Mappings, which contains the vetted structured abstract labels and their mapped-to NlmCategories, i.e., BACKGROUND, OBJECTIVE, METHODS, RESULTS, CONCLUSIONS. NLM will continue to create the NLM category mapping file. New labels with the "UNASSIGNED" NlmCategory may eventually be mapped and added to future versions of the NLM Category Mappings file.