How many records are in Medline?

This question was asked recently in the expert searching e-list. This is a frequent question and one that remains of interest. I first wrote this blog post in 2006 so it is time to update.

The new PubMed is currently running alongside legacy PubMed so I tried these PubMed searches in both. Theoretically the results should be the same. To find out how many systematic reviews are in PubMed’s Systematic Reviews database subset, type: systematic[sb]. New PubMed: 145802 Legacy PubMed: 145870. I then tried the search filter that systematic[sb] is short for. Results: New PubMed: 145766 Legacy PubMed: 145870 Why is this happening? I’ll post this to expert searching e-list to see if I can get any answers.

I did the same experiment for the Clinical Queries RCT therapy/narrow focus filter by copying the search strategy into the search box: New PubMed: 545503 Legacy PubMed: 545543. Different again!

What about finding full text? In the PubMed search box, type: full text [sb] New PubMed: 21453189 Legacy PubMed: 21455734. Something strange is going on, right? Can someone else do these experiments and report in the comments?

To find out how many records there are in OVID Medline, type: docz.dz The current number is 30551310. The PubMed homepage says the database comprises over 30 million records. Last October, it was over 29 million!!