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Why is Searching PubMed in Late Autumn Different than Any Other Time of the Year?

PubMedReloadThe answer is simple and yet complex.

From mid-November to mid-December, the National Library of Medicine (NLM) does year-end-processing. During this time, extensive maintenance is done on MEDLINE. MEDLINE is the NLM database of biomedical journal citations and is the primary component of PubMed.

Daily “routine maintenance” on MEDLINE happens throughout the year and includes a variety of edits to MEDLINE citations. These edits include corrections of misspellings; the addition of published errata, retractions, and comments (including author replies); changes to journal titles and their abbreviations; changes to supplementary concepts such as chemicals, protocols, and diseases; and adjustments to MeSH (Medical Subject Headings).

The primary purpose of year-end maintenance is to update MeSH. Each year, new MeSH headings are added, other headings are replaced with more up-to-date terminology, and out-dated headings are deleted with no replacement. From mid-November to mid-December, NLM applies these MeSH heading changes to MEDLINE citations where necessary.

Things you should know when searching PubMed during the year-end-processing period:

Things you should know when searching PubMed after the year-end-processing period:


For more information, send an e-mail to Ask a Librarian or call the HSLS Main Desk at 412-648-8866.

~ Charlie Wessel

Posted in the December 2013 Issue