NEWS FEATURES, political commentaries and institutional reports incessantly berate the sexual excesses of modern teenagers. "Reports of young studs 'playing rape' … during recess, of 9-year-old sexual harassers and fifth-grade rapists and sodomists have become too common to pass off as simply anomalous," wrote conservative Manhattan Institute researcher Kay Hymowitz. The progressive Media Education Foundation, which distributes educational videos, warned in "Deadly Persuasion" of "widespread and increasing violence against women" by young men incited by brutal, misogynist popular culture and corporate advertising.

Evidence supporting the claims of rising teenage sexual violence is seldom offered. Commentators instead ask, given today's salacious ads, slutty preteen styles, women-hating rap lyrics, MySpace.com, designer porn and binge-drinking orgies, how could young people not be "hooking up" more randomly, more violently and younger?

Yet crime reports, victimization surveys and public health measures consistently reveal something else: large declines in the percentages of young women reporting violence against them, especially sexual attacks, and of young men committing rape and other violent offenses.

The U.S. Justice Department's National Crime Victimization Survey (considered our best measure of crime because its anonymous surveys capture offenses not reported to police) reports that rape has been falling dramatically for decades. The first survey, in 1973, estimated that 105,000 females, ages 12 to 24, were raped that year. In the 1980s and early 1990s, the survey was expanded to include sexual assault and attempted or threatened offenses. Even so, the latest survey (in a young female population 1 million larger than in 1973) reported that 30,000 females, ages 12 to 24, were raped and 60,000 were victims of attempted rape or real or attempted sexual offenses (including verbal threats) in 2005.

The crime surveys further indicate that the decline in sexual violence is greater among younger females than older women. In the last dozen years, they found that sexual victimization rates among girls ages 12 to 19 fell by 78% and among women ages 20 to 24 by 70%, nearly double the drop among women older than 25.

The decrease in violence is reflected in big drops in teenage rape arrests. Led by decreases of 90% in San Francisco, 85% in Orange, Riverside and Ventura counties, and 80% in Los Angeles, San Bernardino and Sacramento counties, California's teen rape-arrest rate fell by 70% over the last three decades. Fewer teens were arrested for rape in 2005 (236) than in 1957 (331), the first year statistics were reported, in a teenage population just one-third today's.

But can we trust these statistics? Rape is an underreported crime: Only four in 10 victims told the National Crime Victimization Survey that they had reported their rapes to police. But rape is less hidden than before. Thanks to feminist campaigns, laws have been extended to criminalize nonconsensual sex with intoxicated, disabled, same-sex and acquaintance victims and other offenses that narrower rape laws excluded. All this makes the recent declines in teenage sexual violence even more impressive.

Why has rape and violence against women, particularly younger women, declined so dramatically over the last generation?

Little research exists on this question, and tentative explanations — from tougher sentencing of violent offenders to pornography's effects in sublimating violence — are not persuasive.

The three-decade decline in teenage and young-adult rape accompanies huge drops in all crimes — murder, assault, drug abuse and property — committed by youth. And get-tough policies designed to imprison more teenagers don't seem to be a factor either. Just-released California Division of Juvenile Justice figures show that fewer youths are locked up today than in 1959, when numbers were first reported.

The most likely explanation involves impressive generational developments. In 1970, women made up one-third of all college students (versus 57% today), earned about one-fourth of all young-adult income (versus nearly half today) and made up small fractions of doctors and lawyers (versus majorities of new entrants into these fields now). Women's rapidly rising status and economic independence in the larger society fostered new attitudes and laws that rejected violence against women.

That younger people growing up in this environment of greater gender equality should show the biggest decreases in rape, while older generations lag behind, is consistent with this explanation. The youngest teenagers (presumably those raised with the most modern attitudes) show the biggest declines of all. Over the last 30 years, rape arrest rates have fallen by 80% among Californians under age 15, much larger than the 25% drop among residents age 40 and older.

Ultimately, however, sexual violence remains a serious danger. That is the best reason for rigorously scrutinizing its real patterns and trends (rather than taking tiresome potshots at "young people" and "popular culture") to learn how to further reduce it.