Abstract
Subjects who indicated that they would volunteer for a psychological experiment reported significantly moTe coffee and caffeine-pill usage than nonvolunteers. Male volunteers more frequently reported cigarette smoking. In this study, males and females each scored significantly higher on the following MMPI scales: paranoia, schizophrenia, hypomania, cigarette smoking, control and social-participation scales. Male volunteers scored significantly higher on the masculinity-femininity and dominance scales, while the male nonvolunteers scored higher on the quantitative orientation scale and the social introversion scale. Female volunteers scored significantly higher on the psychopathic deviate, psychasthenia, F, and manifest-hostility scales; and significantly lower on the lie, defensiveness, and responsibility scales. The results suggest that a personality trait of arousal seeking could explain some of the MMPI scale score differences as well as the central-nervous-system-stimulant usage. The results were concordant with most earlier studies in finding differences between volunteers and nonvolunteers on one or more psychological variables.