In 1979, Groth and Birnbaum developed a typology of rapists, derived from their work with people who had been arrested, convicted, and imprisoned for sex crimes. Factors that were considered to construct their typology included the offender's motivation and the degree of aggression exhibited by the offender. Victim/witness statements, responding-officer statements, modus operandi of offenders, and prior criminal histories informed these factors. It is important to recognize the limitations of this typology as it is based on data acquired from imprisoned sex offenders. As we have learned, most sex crimes are never reported to police, and there are likely systematic differences between imprisoned and non-imprisoned rapists.
Groth's Typology consists of three primary categories: the power rapist, the anger rapist, and the sadistic/ritualistic rapist.
As the name suggests, power rapists are primarily motivated by power. Men in this category are interested more in having control over their victims and "possessing" them than they are interested in causing physical harm to the victim. They do not use force beyond what is necessary to commit the rape. They exhibit anger only in response to victim resistance/fighting back, but will use any amount of force necessary to accomplish their goal, including verbal intimidation, use of a weapon, or actual physical force. Power rapists will sometimes flee the scene if a victim fights back. Power rapists often feel inadequate, controlled by others, or insecure about their masculinity, so they use rape as a means of feeling more powerful, strong, or in control. Power rapists have sometimes been divided further into two sub-categories: