To be honest the biggest thing I remember from psych testing class was it works on average well for some (doesn't matter what test type), but there is a flawed percentage of some registering as the opposite of who they truly are. Eg many fields now have a psych entry exam for employment. (Had a mate go through one recently). It was down to him and one other. In every single way they apparently were the same, hence the psych exam as they couldn't decide who would be best for the job. One manager thought my mate, HR / psych thought the other guy, who DID get chosen. A couple weeks later they ring my mate asking if his still keen. The original guy accepted the job, was sent papers to sign up and then simply ignored every communication. They eventually get hold of him and he simply states, nar not interested. Now for 2 guys who are apparently on par in every single way, they didn't seem that similiar after all. (The only reason the other guy was even chosen was history in selling items where as my mate sold services).