Differentiation by phallometry

Objective: The purpose of this study was to examine the ability of phallometry to discriminate between homicidal child molesters (HCMs), nonhomicidal child molesters (CMs), and controls. Method: Thirty-one HCMs who had committed or had attempted a sexually motivated homicide, 189 CMs, and 47 normal-controls were compared on demographic variables and phallometric responses.

The Pedophile Index (PI) was computed by dividing the highest response to the child initiates or child mutual stimulus by the highest response to an adult consenting stimulus. The Pedophile Assault Index (PAI) was computed by dividing the highest response to an assault stimulus involving a child victim by the highest response of the child initiates or child mutual stimulus.

Results: HCMs, CMs, and controls were not significantly different on Age or IQ. CMs had significantly higher PI scores than controls. Significantly more HCMs (51.9%) and CMs (46.7%) had PI scores equal to or greater than 1.0 compared to controls (27.7%) and HCMs had significantly higher PAI scores than both CMs and controls. Furthermore, significantly more HCMs (63.0%) than either CMs (39.9%) or controls (36.2%) had PAI scores equal to or greater than 1.0. Within-group analyses revealed that of the three groups, only the CMs exhibited a significant difference between their PI and PAI scores with their PI scores being higher.

Conclusions: Consistent with past research, the PI is useful in differentiating HCMs and CMs from controls and the PAI is able to differentiate HCMs from CMs and controls. DD: Looking at those numbers, we cannot do much more than record them - the differences between the groups are too small to appoint values to. In particular, if the PI actually would be a good measure of pedophile interest, the conclusion must be that even if we extend the definition of 'pedophile' to include 25% of all men, still half of all incarcerated child molesters are not pedophiles! Interestingly, the non-homocidal child molesters did not have a higher PAI score than the 'normal subjects'.

source: Ph. Firestone, J.M. Bradford, D.M. Greenberg, K.L. Nunes: Differentiation of Homicidal Child Molesters, Nonhomicidal Child Molesters, and Nonoffenders by Phallometry. American Journal of Psychiatry 157:11, pp. 1847-1850; November 2000