Measuring Frequency

Crime analysts measure crime rates in several different ways, and the distinction between “incidence” and “prevalence” is vital to understanding crime studies.

Incidence gives a snapshot of how many crimes take place during a particular period of time — often a year.

Prevalence measures how many people experience a particular crime during their lifetimes.

Incidence focuses on a particular time period. Prevalence focuses more on those people affected by a crime. This is important with regard to rape because it is so traumatic that it often affects people for years afterwards, or even for their entire lifetimes.

Forcible Sex Offenses Reported by American College Students to Campus or Local Police
Year200420052006
Number of Reports3,7013,6053,459

Source: U.S. Department of Education. Figures include incidents on and off campus. Figures do not include nonforcible sex offenses such as statutory rape or incest.

One measure of incidence is provided by the U.S. Department of Education. The number of reported forcible sex offenses on American campuses has declined in recent years, according to crime statistics compiled by the U.S. Department of Education.

Total enrollment at U.S. degree-granting institutions in 2005 was 17.5 million students; about 0.02 percent of enrolled students reported forcible sex offenses to campus police or local police that year.

Underreporting and Other Difficulties in Measuring Sexual Assaults

Many experts believe that rape and other forms of sexual assault are among the most underreported crimes.

One survey of college students, which relied on student self-reports, not crime reports, found that about 3 percent of all college women become victims of either completed or attempted rape in a given nine-month academic year.

The numbers seem low, but 3 percent translates into 30 such crimes for every 1,000 women students. For a campus with 10,000 female students, the number would reach 300.

An earlier study found a sexual assault victimization rate of 21.6 per 1,000 students.

Unfortunately, researchers have been unable to determine the precise incidence of sexual assault on American campuses because the incidence found depends on how the questions are worded and the context of the survey. For example, researchers did two parallel surveys of American college women during the same time and came up with very different results. The surveys, conducted between February and May 1997, asked only about sexual assaults that had taken place “since school began in fall 1996.”

One survey found a completed rape rate of 1.7 percent, while the other study found a 0.16 percent rate. Similarly, one study found an attempted rape rate of 1.1 percent, while the other study found a rate of 0.18 percent. Thus, the percentage of the sample that reported experiencing a completed rape in one study was 11 times the percentage in the other study. Researchers believe the disparity arises from the way the survey questions are worded.

Regardless of which studies are most accurate, the often-quoted statistic that one in four American college women will be raped during her college years is not supported by the scientific evidence. Nonetheless, several studies indicate that a substantial proportion of female students — between 18 and 20 percent — experience rape or some other form of sexual assault during their college years.

Definitions may vary. The most accurate way to measure rape incidence is a subject of considerable debate. Some scholars contend that the definition of rape and the survey questions used to measure rape may be too broadly worded or poorly phrased. As a result, they count as rape a wide range of actions, some of which may not be criminal. Responses to survey questions will depend on how a term is defined, and how a woman interprets the definition.

Surveys of college students confirm that many sexual assaults are not reported to the police. Researchers asked students why they did not report the incidents to law enforcement officers. The most commonly reported response — offered by more than half the students — was that they did not think the incident was serious enough to report. More than 35 percent said they did not report the incident because they were unclear as to whether a crime was committed or that harm was intended.

Alcohol and drug use affects reporting. Researchers in one study asked students to distinguish between forced sexual assault and incapacitated sexual assault involving drugs and alcohol. They asked:

“Has someone had sexual contact with you when you were unable to provide consent or stop what was happening because you were passed out, drugged, drunk, incapacitated, or asleep?”

Those who answered “yes” to the question were placed in a category called “incapacitated sexual assault” for purposes of the survey — as opposed to the “forced sexual assault” category.

In the incapacitated group, 50 percent said they did not report the incident because they felt partially or fully responsible for what happened, 29 percent said they did not report the incident to the police because they did not want anyone to know, and 31 percent said they did not remember or know what really happened. Survey participants could offer more than one reason.

Men are the assailants, and women the victims, in most rapes and other sexual assaults. Although men sometimes report being assaulted by women, and same-sex assaults take place, most sexual assaults involve men as perpetrators and women as victims. Surveys of men and women on college campuses show a striking disparity in the proportion of women who report being assaulted and the proportion of men who report (even anonymously) being perpetrators. For example, in the Campus Sexual Assault survey, 19 percent of the women reported experiencing a completed or attempted sexual assault since entering college, while 2.5 percent of the men reported being perpetrators. The disparity could arise from various causes:

  • Some people may not give accurate answers to survey questions.
  • Men and women may have different perceptions of the same incident.
  • Experts speculate that rape and other sexual assaults may be like other crimes inasmuch as a relatively small number of people commit serious crimes, but those who do often become repeat offenders.
Date Created: October 1, 2008