The National Institute of Mental Health analyzed the Epidemiologic Catchment Area (ECA) data to determine the percentage of adults who have severe mental illness. (In some studies the term "severe and persistent mental illness" is used as an equivalent.) This definition is based on the specific psychiatric diagnoses as well as the duration and severity of the symptoms. People who, during the prior year, had disorders that are usually accompanied by psychotic symptoms (schizophrenia, and severe forms of bipolar disorder) were included in the severe mental illness category. In addition, people with other diagnoses (major depression, panic disorder, and obsessive-compulsive disorder) were included in the severe mental illness category only if there was evidence that the disorder had been disabling in the past year. Using this definition, about 2.8% of the U.S. adult population are estimated to have a severe mental illness. Schizophrenia (1.5%) major depression (1.1%), and bipolar disorder or manic depressive illness (1.0%) were the most common disorders among people with severe mental illness.
Source: National Advisory Mental Health Council (1993)
Surveys: Epidemiologic Catchment Area (ECA), 1980-85