Here you go Bill:
From The American Journal Of Psychiatry.
Rape: power, anger, and sexuality
AN Groth, W Burgess and LL Holmstrom


Accounts from both offenders and victims of what occurs during a rape suggest that issues of power, anger, and sexuality are important in understanding the rapist's behavior. All three issues seem to operate in every rape, but the proportion varies and one issue seems to dominate in each instance. The authors ranked accounts from 133 offenders and 92 victims for the dominant issue and found that the offenses could be categorized as power rape (sexuality used primarily to express power) or anger rape (use of sexuality to express anger). There were no rapes in which sex was the dominant issue; sexuality was always in the service of other, nonsexual needs.


http://ajp.psychiatryonline.org/cgi/content/abstract/134/11/1239