I'm only talking about myers briggs here, but I'm really confused about why you say the tests seem to work. They don't seem to work to me. I can get any of handful of different results and so can many people I know. Not only that, but I've studied the underlying theory enough to know that a lot of people I've met who only go by the tests are mistyped. They don't even know what the letters mean. They don't know if they use extroverted or introverted thinking/intuition/feeling/sensing. They think that if they're smart, they have to have a T in their type.