We made a freetext search on headache in Pubmed with limits to entrez date 60 days which returned 442 records. We checked the availability of the PubMed records (in descending order) in Google Scholar until we reached the possible breakpoint and then checked the EDAT which is the date and time when the record was added to PubMed.

Google Scholar has indexed 1 of 5 articles published 2005/12/29 09:00 GMT-8. The screenshot below shows both the Google Scholar reference and a clipping from part of the PubMed reference:

From 2005/12/28 09:00 and descending one following day everything was indexed, with the exception of one article.

PMID 16375021 from 2005/12/27 doesn’t exist in Google Scholar, but the rest of the articles from the same date exist.

From 2005/12/31 09:00 and ascending at least one following date nothing was indexed by Google Scholar (2005/12/30 had no records in this search).

This means thet Google Scholar, at least in this single test 2006-02-01 11:00 GMT+1, has an update gap of more than one month. I did a similar undocumented test in 2005-10-07 which showed a latest update in Google Scholar 2005-08-17. To discover if the updates of PubMed via Google Scholar is regular or unregular requires regular tests during a longer time period.