Filtering Data

[Dee]

I have a spreadsheet that contains a column for
Investigator Name, Pt. ID and Date of Enrollment as
follows. I need to filter how many patients were
enrolled by each site per month. Should I use an
advanced filter, I'm not sure how to do this. Any help
would be greatly appreciated.

Investigator Pt. ID Date
Dr. Black
01-001 08/09/03
01-002 08/09/03
01-003 08/12/03
01-004 08/13/03
Dr. Smith
03-001 08/16/02
03-002 08/16/02
03-003 09/06/02
03-004 09/06/02
03-005 09/06/02
03-006 09/20/02

Regards,
Dee