The Bureau of Justice Statistics said that "intimate partner violence" rates fell by more than 50 percent. The decline mirrored a decade-long trend in other violent crimes, and the department did not suggest a cause.
"There's still generally no consensus about why any crime in general has dropped," said Shannan Catalano, the study's author. "It's safe to say it's more than one factor that went into it."
Some experts attribute the decline to better training for police and more funding for prosecution, two key elements of the 1994 Violence Against Women Act. Investigators increasingly are better trained to handle abuse cases and bring them to court.
"For the first time, there are entire domestic violence units in law enforcement," said Lonna Stevens, director of the Sheila Wellstone Institute, a Minnesota-based domestic violence organization. "We've had protocols and policies developed for responding to this."
In 1993, there were about 5.8 incidents of nonfatal violence for every 1,000 U.S. residents above the age of 12. By 2004, that number had fallen to 2.6, the agency said. Homicides fell by about 30 percent, from 2,269 in 1993 to 1,544 in 2004.
The Justice Department defines intimate partner violence as violence by a current or former spouse, boyfriend or girlfriend or a same-sex partner.
Stevens said police have been less successful responding to and deterring abusive behavior in some minority communities, where racism and cultural differences can keep reporting rates low.
Over the 12-year reporting period, about 18 out of every 1,000 American Indian and native Alaskan women were victimized — a violence rate three times higher than among white women.
Black women were more likely than white women to be abused but the study also found that they were more likely to report their abuse to the police than white women.
Women in their early 20s and women who were divorced or separated had the greatest risk of being abused, the study found. Violence was also more common in low-income households.
Asian males, white males and the elderly reported the lowest rates of partner violence.