BOSTON — A comprehensive study of suicidal thinking among college students found more than half of the 26,000 surveyed had suicidal thoughts at some point.

The Web-based survey in spring 2006 used separate samples of undergraduate and graduate students from 70 colleges and universities. Of the 15,010 undergraduates, 55 percent had ever thought of suicide; 18 percent seriously considered it; and 8 percent made an attempt. Among 11,441 graduate students, exactly half had such thoughts; 15 percent seriously considered it and 6 percent made an attempt.

"Suicidal crises are a common occurrence on college campuses," says Chris Brownson, director of the University of Texas Counseling and Mental Health Center in Austin and one of the study's researchers.

"Previous research has indicated the severity of mental health issues on college campuses has been increasing," Brownson says. "When you look at the lifetime prevalence rates, those are alarming statistics."

The findings, presented Sunday at the American Psychological Association's annual meeting, were compiled from online surveys conducted by the National Research Consortium of Counseling Centers in Higher Education at UT-Austin.

In the 12 months before the survey, 6 percent of undergraduates and 4 percent of grad students reported seriously considering suicide. More than half of these episodes lasted a day or less. The reasons for suicidal thinking varied. Emotional or physical pain was the top reason; others were romantic relationship troubles and school-related problems.

Whether there are more disturbed students in college today is a subject of debate. Experts say more young people with mental health problems are able to attend college as a result of better medication and other treatment; more women attend, and they are more likely to seek help; and colleges have improved tracking of people who have needed help with mental health.

"Most people in university environments don't really appreciate how much suicidality students engage in," says lead researcher David Drum. "We really need to keep rescuing those in need, but we need to be shifting some of our focus to building resilience and resistance to ever engage in these thoughts."