Occasionally policymakers and activists will talk about how the justice system needs to keep mentally ill people out of prisons. If it did that, prisons would be very empty indeed. A new Urban Institute report points out that more than half of all inmates in jails and state prisons have a mental illness of some kind:

Percent of Inmates Who Have Mental or Mood Issues

James and Glaze 2006/Urban Institute

The most common problem is depression, followed by bipolar disorder.

Types of Mental Issues Among State and Federal Inmates

U.S. Department of Justice, Bureau of Justice Statistics 2007 /Urban Institute

The numbers are even more stark when parsed by gender: 55 percent of male inmates in state prisons are mentally ill, but 73 percent of female inmates are. Meanwhile, the think-tank writes, "only one in three state prisoners and one in six jail inmates who suffer from mental-health problems report having received mental-health treatment since admission."

An increasingly popular program might help thin the ranks of these sick, untreated inmates. What are known as "mental-health courts" have sprung up in a number of states as an alternative to incarceration. A shoplifter who has, say, schizophrenia might be screened and found eligible for mental-health court, and then be sentenced to judicially supervised treatment. These types of courts have expanded rapidly since 2000, and there are now hundreds around the country.