Reliability and validity of the DSM-IV diagnostic category of schizoaffective disorder: preliminary data

Concerns have been expressed about the reliability and validity of the DSM-IV criteria for schizoaffective disorder, but no systematic study has been published up to now.

The Cohen's kappa for the individual items of the DSM-IV definition of schizoaffective disorder, manic episode and major depressive episode was evaluated in 150 patients independently interviewed by two psychiatrists using the Composite International Diagnostic Interview. The two-year outcome of patients with a consensus DSM-IV diagnosis of schizoaffective disorder was compared to that of patients with DSM-IV schizophrenia and schizophreniform disorder, using the Strauss-Carpenter Outcome Scale.

The Cohen's kappa was 0.22 for the diagnosis of schizoaffective disorder, 0.71 for that of manic episode, and 0.82 for that of major depressive episode. Schizoaffective patients had a significantly better outcome than those with schizophrenia but a worse outcome than those with schizophreniform disorder.

The inter-rater reliability of the DSM-IV criteria for schizoaffective disorder is not satisfactory. The better outcome of DSM-IV schizoaffective disorder compared with schizophrenia seems to depend more on the inclusion, in the definition of schizophrenia but not in that of schizoaffective disorder, of the six-month duration and functional impairment criteria than on the different symptomatological patterns of the two conditions.

The size of the sample of patients fulfilling DSM-IV criteria for schizoaffective disorder was small.

The study suggests that the clinical implications of the currently problematic diagnosis of schizoaffective disorder may be modest.