|April 19, 2002 [posted]
|Why Citations to Older Articles May Display Before More Recent Ones in PubMed®
ome users have asked us why citations to older articles sometimes display ahead of newer ones in PubMed. The answer has to do with PubMed's Entrez date and when citations are added to the database.
PubMed results are initially displayed in reverse chronological order of the Entrez date, i.e., last in, first out. If desired, search results can be sorted by publication date instead using PubMed's Sort feature. The publication date is the date the article was published and is determined by the journal publisher.
Citations are generally added to PubMed soon after publication. However, there are many instances when citations are not added to PubMed until after the date of publication. This results in older citations receiving an Entrez date that is noticeably more recent than the date of publication.Citations for older publications can be added to PubMed for the following reasons:
The American Journal of Geriatric Cardiology began publication in 1992. NLM started indexing this journal for MEDLINE in 2001. The publisher subsequently submitted back issues to 1992 which appear in PubMed with the "as supplied by publisher" status tag and display in the order of the date they were added to PubMed.
By Annette M. Nahin
Nahin AM, Tybaert SJ. Why Citations to Older Articles May Display Before More Recent Ones in PubMed®. NLM Tech Bull. 2002 Mar-Apr;(325):e3.