Failure to differentiate bipolar disorder from schizophrenia on measures of neuropsychological function

30 inpatients diagnosed with schizophrenia were compared to 35 inpatients with bipolar affective disorder, manic type, on a large group of neuropsychological measures. Separate factor analyses were performed on measures of verbal, spatial, and speed variables in order to generate summary scales. Controlling for the effects of age, education, sex, duration of illness, number of previous hospitalizations, and medications at time of testing, there were no significant differences between diagnostic groups on the three factors or on individual test variables. Patients on medication performed more poorly on speed variables than those off medication. These findings call into question the notion of differential patterns of cognitive deficit among psychotic diagnoses.