The study, which was conducted in the Chicago region, is the largest and most methodologically sophisticated of its kind. The rates established by the researchers are much higher than the estimated 15 percent of youth in the general population thought to have psychiatric illness --- and the study findings place detained youth at roughly the same level as those already identified as at highest risk, including abused and runaway adolescents.

Because previous studies of youth involved with the legal system had yielded
inconsistent results, the research team tried to gauge the true extent of the problem by employing a large, stratified sample, randomized design, and standardized diagnostic measures. They assessed psychiatric disorders in 1,829 African-American, non-Hispanic white teenagers and Hispanic teenagers, ages 10 to 18 years, who were randomly selected at admission to an urban juvenile temporary detention center. About 90 percent of admitted youths were male. Masters-level psychologists conducted a structured diagnostic interview with the selected teens, documenting the six-month prevalence rates of various disorders.

About half of the detained teens abused or were addicted to drugs, and more than 40 percent had disruptive behavior disorders: oppositional defiant disorder and conduct disorder. Even when conduct disorder (common in this population) was excluded, nearly 60 percent of males and more than two thirds of females met diagnostic criteria for, and were functionally impaired by, one or more mental or substance use disorders. Overall, disorders were more prevalent among older youth and females, more than 20 percent of whom had a major depressive disorder.

There was some variance in individual prevalence rates among different racial and ethnic groups. Among boys, non-Hispanic white youths showed the highest rates of most disorders, and African-Americans the lowest. The only categories for which boys showed higher rates than girls were for a manic episode, psychotic disorders, any substance abuse disorder, and marijuana use disorder.

"We are especially concerned about the high rates of depression and dysthymia among detained youth -- 17.2 percent of males, 26.3 percent of females," wrote the authors.

They also noted that in tight economic periods, it may be particularly important for mental-health professionals to maintain a high index of suspicion for problems among this population because the legal and social systems are poorly equipped to identify or treat youths with mental illness.