A Comparison of Volume and Circumference Phallometry: Response Magnitude and Method Agreement

Abstract

Penile circumference and penile volumephallometry are laboratory methods of assessing sexualarousal. Volume phallometry is reportedly more sensitiveto responses, but comparative studies have beeninconclusive and beset with methodological problems. In thisstudy, 42 self-professed heterosexual volunteers wereassessed with both methods simultaneously, employing astandard test for erotic partner preference. Pearson correlations between test outcomeprofiles were very high (r > .80) for subjects whosecircumferential increase was >2.5 mm [10% of a fullerection (FE)]. However, among lower responders the agreement dropped precipitously (mean r =–.15). Moreover, as a group higher respondersdifferentiated adult and pubescent age female stimulifrom each other and all other categories with eithermethod, but lower responders made this differentiationonly with the volume method. We conclude that (1) athigh levels of response both methods are equally good,(2) at low levels of response volumetric phallometry is a more accurate measure of arousal, and (3)10% FE, or a 2.5-mm circumference increase, should bethe minimum response criterion for the circumferentialmeasure.