COLUMBUS, Ohio - At a time when colleges and universities are under pressure to combat sexual assault, a new survey offers a sharper picture of just how widespread the problem is.

Of the 150,000 female students who responded to a survey of undergraduate woman, nearly a quarter said they had experienced unwanted sexual contact sometime during college.

The survey had been sent to nearly 780,000 students at more than two dozen universities.

The results are generally in line with other surveys. And they confirmed that alcohol and drugs are important risk factors.

The survey found freshman women appeared to be at greater risk than older students for these forced or incapacitated encounters. About 17 percent of freshman females reported sexual contact that was forced or while incapacitated; for senior-year students, the percentage had dropped to 11 percent.

Some of the schools involved said the survey results will boost their ongoing efforts. Dartmouth says it's forming a committee of students, faculty and staff to analyze the data.