A comparison of volume and circumference phallometry: Response magnitude and method agreement

Penile circumference and penile volume phallometry are laboratory methods o f assessing sexual arousal. Volume phallometry is reportedly more sensitive to responses, but comparative studies have been inconclusive and beset wit h methodological problems. In this study, 42 self-professed heterosexual vo lunteers were assessed with both methods simultaneously, employing a standa rd test for erotic partner preference. Pearson correlations between test ou tcome profiles were very high (r > .80)for subjects whose circumferential i ncrease was > 2.5mm [10% of a full erection (FE)]. However; among lower res ponders the agreement dropped precipitously (mean r = -.15). Moreover as a group higher responders differentiated adult and pubescent age female stimu li from each other and all other categories with either method, but lower r esponders made this differentiation only with the volume method. We conclud e that (1) at high levels of response both methods are equally good, (2) at low levels of response volumetric phallometry is a more accurate measure o f arousal, and (3) 10% FE, or a 2.5-mm circumference increase, should be th e minimum response criterion for the circumferential measure.