This study was one of the first to explore misdiagnosis of black and Hispanic patients as a potential explanation for race patterns in the rate of schizophrenia in treatment samples. Using data collected from the outpatient department of an inner-city municipal hospital center (January 1980 to June 1981), the authors assessed whether minority patients with bipolar disorder were more likely than white patients to have been previously assigned a diagnosis of schizophrenia. The study sample was based on patients who were enrolled in a psychopharmacology program and were assigned DSM-III diagnoses of bipolar disorder at admission to this program. Previous inpatient diagnoses were evaluated.

Among the 76 patients sampled for this study who had had previous hospitalizations, 68.4% had a previous diagnosis of schizophrenia: 51.3% of the 37 whites, 85.7% of the 21 blacks and 83.3% of the 18 Hispanics in the study. Multivariate analyses showed that the presence of auditory hallucinations and younger age at first hospitalization were both associated with having a previous diagnosis of schizophrenia, and that ethnic group remained significant after adjusting for the effects of these two variables (with blacks and Hispanics having higher number of "misdiagnoses"). Having been treated by a psychiatrist of the same ethnicity did not protect black or Hispanic patients from such misdiagnoses.

Subtypes of schizophrenia were also compared, and the authors found that blacks were significantly more often previously diagnosed with paranoid schizophrenia than either whites or Hispanics, despite their having similar number of occurrences of persecutory delusions, ideas of reference, anger/irritability, and violent/destructive behaviors. Whereas 7 of the 18 whites and 6 of the 15 Hispanics who had persecutory delusions were previously diagnosed with paranoid schizophrenia, all of the 12 blacks with persecutory delusions were previously "misdiagnosed." Similar patterns were noted with bizarre delusions.

The study found that blacks were more likely to experience any delusion or hallucination than whites, which could help to explain the misdiagnosis patterns. The authors suggest that these patterns may indicate that blacks with mania are hospitalized at more severe stages of their disease. Alternatively, the high occurrence of psychotic symptoms among the blacks and Hispanics may reflect the lower threshold of psychiatrist evaluating these symptoms in these patients, probably as a result of an assumption of a schizophrenia diagnosis.

The authors conclude that ethnicity is a significant factor in the misdiagnosis of bipolar patients as schizophrenic.