The most violent prisons in the Texas state system share a common factor: They house a high proportion of mentally ill inmates. The Texas Tribune analyzed violent-incident data from 99 state prisons from 2006 to 2012, and found far more incident reports at facilities housing high numbers of mentally ill, violent offenders than at other prisons. Among the five units with the highest number of reports are the state’s three psychiatric facilities. In addition, the William P. Clements Unit, which is not a psychiatric facility, but houses 1,800 mentally ill inmates among a population of 3,500, is in that group, according to Texas Department of Criminal Justice data.