Hare's Psychopathy Checklist Revised (PCL-R) is (from what I've learned in psychology class...but I'm not an expert or anything) a list of traits that the psychologist matches onto a person. The list is composed of 20 items which are rated from 0-2 (weak-strong) by the psychologist. This means that the highest possible score is 40, with 40 being a "prototypical psychopath". A score of 30 or higher on the PCL-R is the diagnostic criteria for psychopathy under the DSM-IV.