Susan, a twenty-three-year-old student, went to answer a knock at her door and found a man she knew from one of her afternoon college courses. When she opened the door to let him in, he overpowered her, threw her on the couch, and raped her.

According to researcher Mary P. Koss, incidents like the above are more common than is generally reported. In a national sample of college students, for example, Koss and her colleagues discovered that 15 percent of women respondents had been raped, while an additional 12 percent had experienced attempted rape. These findings, Koss asserts, mean that at least one out of every four college women is a victim of rape or attempted rape. In another widely cited study, researcher Diana E.H. Russell interviewed a random sample of 930 San Francisco women about their lifetime experiences with physical and...