Personality characteristics of long and short sleepers.

College students categorized as either long sleepers (mean = 9.25 hours per day) or short sleepers (mean = 6.2 hours per day) were administered a variety of personality tests. With a multiple regression analysis the patterns on the MMPI of higher MA and F with a lowered PD and CI (number of critical items) most significantly differentiated the short from the long sleepers. Also of relevance was the finding that long sleepers were more likely to score in the pathological direction on most of the MMPI clinical scales.