Reliability issues in the penile assessment of incarcerants

Although there has been increased reliance upon the direct physiological measurement of penile tumescence in the assessment of sexual deviations, the reliability of these measures has never been empirically validated. This investigation evaluates the reliability of the rape index as a technique in differentiating rapists from nonrapists. Eighteen individuals incarcerated on non-sexual-related offenses were presented visual and audio stimuli depicting mutually consenting intercourse, rape, and aggression. These stimuli were presented under two instructional sets: (1) enchance arousal and (2) suppress arousal. Reliability indices for the rape index were computed among various conditions of modality presentation, instructional set, and test-retest conditions. The overall reliability of the rape index was found to be low. The implications of these results upon the assessment and classification of offenders is discussed.