Elaine Zahnd, a sociologist at the Public Health Institute, partnered with the University of California, Los Angeles, Center for Health Policy Research in conducting the California Health Interview Survey, which found almost 4 million adults in California reported being a victim of physical or sexual violence from an intimate partner.
One-quarter of the 4 million report being forced by their intimate partner to have sex, the researchers said.
Almost 28 percent of lesbian or gay adults in California report intimate partner violence during their adult lives, 40.6 percent of bisexuals report intimate partner violence and 16.7 percent of heterosexual adults report intimate partner violence, the study said.
"These findings should cause us to reconsider our assumptions about the root causes of violence, even as we redouble our efforts to eradicate it," Zahnd said in a statement.
Women are almost twice as likely to be victims of adult physical violence as men and are eight times as likely to report being the victim of sexual violence since age 18, the study said.