Amid all the commentary on recent mass shootings in the U.S., what is the truth about violence and mental illness? The Pittsburgh Post-Gazette cites a study by Jeffrey Swanson, a psychiatry professor at Duke University and one of the world's leading experts on the subject. After excluding people with substance abuse problems, only 7 percent of those with a serious mental illness -- schizophrenia, depression or bipolar disease -- had committed acts of violence, from shoving someone to shooting someone. among the rest of the population, that rate was just 2 percent.

"The vast majority of people with mental illness are not violent," Swanson said, "but you could take the same study and say people with mental illness are three times more likely to commit a violent act than others are." It does seem that a disproportionate number of mass shootings involve people with mental illness. Mass shootings by definition are tragically dramatic, frightening, and hard to fathom, yet also comprise only a tiny fraction of all homicides, Swanson says. "Most murders are committed by people who are perfectly normal from a mental point of view," added John Csernansky, psychiatry chairman at Northwestern University. "So if an ordinary person shoots his business partner for money or his wife for infidelity, it doesn't hit the papers in the same way. If a person with schizophrenia commits an act of violence and that is driven by their delusion, it's more than likely going to be an act that doesn't make any sense."