Efforts to prevent violence with better mental health screening are unlikely to work very well if at all.

Perhaps most important, although people with serious mental illness have committed a large percentage of high-profile crimes, the mentally ill represent a very small percentage of the perpetrators of violent crime overall. Researchers estimate that if mental illness could be eliminated as a factor in violent crime, the overall rate would be reduced by only 4 percent. That means 96 percent of violent crimes—defined by the FBI as murders, robberies, rapes, and aggravated assaults—are committed by people without any mental-health problems at all. Solutions that focus on reducing crimes by the mentally ill will make only a small dent in the nation’s rate of gun-related murders, ranging from mass killings to shootings that claim a single victim.