Anecdata on disproportionate searching: I'm a middle-class white guy who's 40. I haven't been pulled over for a "random stop, sir" since I was about 25, and before that I would have been pulled over about a dozen times. The times when I was pulled over, I was a young guy with long hair in a beaten-up car. My mother has never been pulled over. And judging from the general dialogue with friends, this is not an unusual experience. These "random stops" are (almost!) certainly using a different definition of 'random' than the ones we used in statistics class.