Caffeine myth

Caffeine's diuretic effect seems pretty self-evident, but this New York Times article offers up proof otherwise. I have one major qualm though. The studies cited used urine output volume as a major determinant for dehydration, but anyone whose gotten through exam periods fueled entirely by coffee and dining hall food realizes there are other ways liquid can be exumed (although I wouldn't want to work on THAT study). There's got to be a better way to measure dehydration.