Impact on MEDLINE®/PubMed® from the PubMed Central® Back Issue Digitization Project
As of April 2007 under the PubMed Central Back Issue Digitization Project, the National Library of Medicine® (NLM®) has digitized nearly 40 journals back to the first volume for each title and has deposited the full text contents in PubMed Central (PMC). Publishers of those titles continue to deposit full text content for current material. This project, funded in part by the Wellcome Trust in the United Kingdom, has yielded the creation of over 70,000 "new" citations, including author abstracts when available, all of which have now been added to PubMed. About 38,000 are from issues that predate 1966 as the date of publication; some date to the late 1800's (e.g., Journal of Anatomy and Physiology). About 32,000 are from issues published from 1966 forward. These consist of issues that predate when the title was selected for indexing (e.g., Texas Heart Institute Journal) as well as those that belong to journals which were or are selectively indexed for MEDLINE (e.g., Plant Physiology, and Proceedings of the National Academy of Sciences).
These 70,000 citations were derived from the PMC data which underwent quality control review. The citations were then moved to the internal Data Creation and Maintenance System (DCMS) which is used by NLM for the MEDLINE citation workflow and from which NLM exports the information to PubMed and journal citation data licensees. These citations are not indexed with MeSH. At the completion of this project, all added citations will carry the citation status label of [PubMed]. While the project is on-going, some post-1965 citations may be held for further review to ensure that the data entry conventions are in line with the general MEDLINE format. These citations would have either [PubMed — in process] or [PubMed — as supplied by publisher], until processing is completed.
Another aspect of this digitization project is adding author abstracts from articles where the equivalent, previously existing MEDLINE/PubMed citation does not have an author abstract. An author abstract is one written by the author(s) and published as part of the article. Approximately 41,000 new abstracts have been added from the group of PMC journals for which full back issues have been completed. These additional abstracts increase text word access points especially for citations originally created for MEDLINE prior to 1975 when abstracts were not routinely included.
This process of supplementing PubMed with both new citations and new author abstracts is now a standard procedure when a PMC journal's back issue digitization is completed.
