Shifts in hospital diagnostic frequencies: bipolar disorder subtypes, 1981-1993.

Annual rates of bipolar and schizoaffective disorder (SA) subtypes from 1981 to 1993 at a private university psychiatric hospital were reviewed. Annual total diagnostic rates for all bipolar disorders (BPD) remained constant between 1981 and 1993, (22%), while the frequency of SA rose 6-fold, from 1.4% to 8.7%. Rates of BPD, not otherwise specified increased 7-fold, while that for the other BPD subtypes fell in the same period of time. Several factors may have influenced these trends including changes in diagnostic criteria used, treatment-oriented diagnostic bias and indirect effects of sharply falling length of stay.