Diagnostic prevalence and comorbidity

Prisons and jails remain a growth industry, with many countries increasing correctional services to cope with the ever-burgeoning inmate population. One longstanding issue is the perceived increase in prevalence of mental disorders that are found in correctional settings compared to the community. Definitions of mental illness and methods of assessment vary substantially. That said, emerging data reflect some consistency in the range of estimated prevalence. Personality disorder (predominantly antisocial personality disorder) is the most common mental disorder among prisoners, accounting for 65% of male and 42% of female prisoners. Estimated rates of psychosis in some settings are as high as 3.7% for males and 4.0% for females, while major depressive disorders are found in up to 10% of male and 12% of female prisoners. Estimated point prevalence rates for alcohol abuse and dependence varied between 18 and 30% for male prisoners and between 10 and 24% for female prisoners; these estimates were between 10 and 48% for males and 30 to 60% for female prisoners with respect to drug dependence and abuse. The rates of almost all disorders are several times higher than those found in the general community, and the rates of comorbidity are exceptionally high. This chapter outlines the best available correctional prevalence of common mental disorders and considers the key assumptions and methodological challenges around ascertaining rates of these different diagnoses.