CHICAGO â A new large study challenges the idea that mental illness alone is a leading cause of violence. Researchers instead blame a combination of factors, specifically substance abuse and a history of violent acts, that drives up the danger when combined with mental illness in what they call an "intricate link." People with serious mental illness, without other big risk factors, are no more violent than most people, according to the study of more than 34,000 U.S. adults. The research was released Monday in Archives of General Psychiatry. "Mental illness can provide the knee-jerk explanation for the Virginia Tech shootings," but it's not a strong predictor of violence by itself, said lead author Eric Elbogen of the University of North Carolina at Chapel Hill School of Medicine. Elbogen compiled a "top 10" list of things that predict violent behavior, based on the analysis. Younger age topped the list. History of violence came next, followed by male gender, history of juvenile detention, divorce or separation in the past year, history of physical abuse, parental criminal history and unemployment in the past year. Rounding out the list were severe mental illness with substance abuse and being a crime victim in the past year. After the 2007 Virginia Tech killings by a student ordered to get psychiatric treatment, some states considered laws adding mental health questions to background checks for gun buyers or denying weapons to people who've been involuntarily committed for mental health treatment. The new research, which bolsters other similar findings, raises questions about such laws, experts said. Such legislation may be both ineffective and discourage people who need help from getting treatment. "We are being misled by our own fears," said Columbia University psychiatry professor Dr. Paul Appelbaum, who wasn't involved in the new study. "We ought to be concerned about providing good treatment and helping people lead fulfilling lives, not obsessed with protecting ourselves from phantom threats that appear to be unrelated to mental illness." U.S. systems to treat mental illness and substance abuse are separate, uncoordinated and could do a better job treating people with both problems, Appelbaum said. For the new study, the researchers analyzed data from the National Epidemiologic Survey on Alcohol and Related Conditions. The original survey in 2001-2002 involved more than 43,000 face-to-face interviews with a representative sample of American adults. Three years later, many of the same people, more than 34,000, were interviewed again. Questions about violence in both interviews included: _"Ever use a weapon like a stick, knife or gun in a fight?" _"Ever hit someone so hard that you injured them or they had to see a doctor?" _"Ever start a fire on purpose to destroy someone's property or just to see it burn?" _"Ever force someone to have sex with you against their will?" From the responses, the researchers determined what elements raised the risk of violent behavior. There were 3,089 people deemed to have severe mental illness _ schizophrenia, bipolar disorder and major depression _ but no history of either violence or substance abuse. They reported very few violent acts, about 50, between interviews. But when mental illness was combined with a history of violence and a history of substance abuse, as in about 1,600 people, the risk of future violence increased by a factor of 10. The relationship between mental illness and violence is there, "but it's not as strong as people think," Elbogen said. Predicting who will act violently is complex, said John Monahan, a psychologist at University of Virginia's law school, who has done similar research but was not involved in the new study. "It is true that our crystal balls are very murky," Monahan said. "The vast majority of violence that occurs in American society has absolutely nothing to do with mental illness." The large national survey, conducted by the National Institute on Alcohol Abuse and Alcoholism, included people living in shelters, hotels and group homes, as well as houses and apartments, but it didn't include people living in hospitals, jails or prisons. Rosanna Esposito of the nonprofit Treatment Advocacy Center in Arlington, Va., applauded the study but pointed out the researchers weren't able to analyze whether the subjects were in psychiatric treatment or not. Medication for serious mental illness can reduce the risk of violence, she said.