A public policy official reads that the rates of violence are five times higher among people with serious mental illness than they are among the general population. Based on this evidence, the public policy official recommends legislation that would allow

those with serious mental illness to be detained preventatively to keep them from committing violent offences. What is the scientific evidence that suggests that such a policy is not justified?

Answer:

The actual risk of violence is much lower than publicly perceived. Ninety percent of mentally ill people have no history of violence. Furthermore, while current psychotic symptoms predict violence, past psychotic episodes do not predict future violence. While the percentage of violent behavior among those with mental illness is higher than it is among the general population, those statistics include those who abuse alcohol or drugs. Substance abuse increases the likelihood of violence for both the mentally ill and the general population. Finally, other factors, such as poverty, also increase the risk for violence, and our society would consider it a violation of civil liberties to detain someone simply for being poor. Except in certain extreme cases, this policy would not be justified.