Two-thirds of all rapes occurred at night, while attempted rapes were more likely to occur during the daytime. A high percentage of rapes occurred in the home of the victim or of the assailant. The highest rape victimization rates were among women 16 to 24 years old. Most victims were married. Three-fourths of rapes involved one victim and one offender. Most offenders were unarmed, although 22 percent of rapes involved the use of a gun or knife. Many victims offered some form of resistance. Most women who resisted were victims of attempted rapes, while most who did not resist were victims of completed rapes. Resistance increased the likelihood of injury to the victim, with the most common injuries being bruises, black eyes, and cuts. The cost of medical care was approximately $104 per injured victim. There are several theories as to why men rape. Ethologistic theory holds that instinctual and biological forces, including hormone levels, trigger antisocial aggressive acts. Reactive theory asserts that frustration causes aggressive behavior and that the aggressive act serves as a form of catharsis. Social learning theory suggests that aggressive behavior is rewarding, while psychological theories attribute aggression in rape to underlying mental problems such as hostility or a need to dominate. 13 references.