I had googled it on my phone, this was the source:
"Hopefully I can be of some help. In the past, there are between 4500 and 5000 primary applications that are received. From those, they send secondaries to 1400-1500 applicants."
Does anyone know how many people receive UCSF secondaries? They say that they interview about 500 people so I'm just wondering. Thanks a lot.
forums.studentdoctor.net
This was an SDN post from 2002, so the numbers appear to have doubled from 4500 to 9000 applicants, and interpolating for this the number of secondaries might be 3000. But a lot changes in 20 years, maybe the number is completely off.