I don't even know. But apparently everybody has their own reality. Which sounds very philosophical, and also like the beginnings of a great fantasy novel. (My reality vs. your reality, in epic pitched battle!)

This pdf (http://www.learningdomain.com/MEdHOME/QUALITATIVE/Reliab.VALIDITY.pdf) is the article I was reading. I admit I'm very biased towards numbers and a universal reality, but I still thought it was dumb.