• To test the contribution of the criterion of six months of illness to the predictive usefulness of the DSM-III diagnosis of schizophrenia, we compared, from a sample of 121 patients with functional psychosis, those who had been ill for six months or more at index but did not meet the nontemporal DSM-III criteria and those who met the full criteria. We found that while the six-month criterion is an important component, it is not the sole reason for the predictive power of these criteria. Many who met only this criterion had relatively good outcomes, and, as a group, their outcomes were only slightly worse than for the entire series of psychotic patients. Those who met the full criteria had a significantly poorer outcome in terms of both continued psychopathology and social functioning.
Helzer JE, Kendell RE, Brockington IF. Contribution of the Six-Month Criterion to the Predictive Validity of the DSM-III Definition of Schizophrenia. Arch Gen Psychiatry. 1983;40(12):1277-1280. doi:10.1001/archpsyc.1983.01790110019004