A large-scale nationwide US survey indicated that more than one fourth of adults had symptoms in the previous 12 months that would qualify for a diagnosis of a psychiatric disorder, and the majority of cases would be considered moderate to serious in severity, according to an article in the June issue of the Archives of General Psychiatry.

Although previous epidemiological surveys have estimated prevalence of mental disorders in the U.S. as high as 30 percent, information on severity and comorbidity had not previously been available, according to background information in the article.

Ronald C. Kessler, Ph.D., of Harvard Medical School, and colleagues analyzed information on mental disorders in the United States collected from the U.S. National Comorbidity Survey Replication (NCS-R), a nationally representative face-to-face household survey conducted between February 2001 and April 2003 using the World Health Organization World Mental Health Survey Initiative version of the Composite International Diagnostic Interview.

The researchers determined the 12-month prevalence of different types of mental disorders as well as the level of severity of the disorder in that 12-month period and the likelihood that an individual qualifying in that 12-month period for a diagnosis for one mental disorder would also meet the criteria for at least one other condition.

Disorders were divided into four classes: anxiety disorders, including panic disorder, post-traumatic stress disorder and obsessive-compulsive disorder; mood disorders, including major depressive disorder and bipolar disorder; impulse control disorder, including oppositional defiant disorder, attention deficit/hyperactivity disorder and intermittent explosive disorder; and substance abuse disorder, defined as alcohol and drug abuse and dependence.

Severity was divided into three levels: serious, which might be defined by criteria including a serious suicide attempt or substantial work limitations as result of the disorder; moderate, which might be defined by criteria including suicide ideation or substance abuse without serious impairment of functioning; and mild.

Based on data obtained from 9,282 adult respondents to the survey, the researchers determined that the 12-month prevalence for any disorder was 26.2 percent, with a 12-month prevalence of anxiety disorders of 18.1 percent; mood disorders, 9.5 percent; impulse control disorders, 8.9 percent and substance abuse disorders, 3.8 percent.

Of the cases, 22.3 percent were classified as serious; 37.3 percent as moderate and 40.4 percent as mild. Fifty-five percent of individuals with a disorder met the criteria for only one disorder, 22 percent for two diagnoses and 23 percent for three or more diagnoses.

"Although mental disorders are widespread, serious cases are concentrated among a relatively small proportion of cases with high comorbidity," the authors concluded.