How to tell when you graduated

DRM 9000: Out of curiosity, Greg, did you graduate college in 1999?
GREG: Yeah... how did you...?
DRM 9000: A simple bell curve analysis of the release dates of your music collection reveals a statistical peak from November '95 to March '99.
DRM 9000: Ergo... class of '99.
GREG: What? No... I've bought a ton of music since college, I... no...
DRM 9000: Your "Pavement/Shins Ratio" also puts you solidly in the '99 bucket.
GREG: Th-there's a Decemberists CD on my dresser! Make sure you counted that!!