• We showed that schizophrenia was a discrete disorder by using a quantitative clinical scale that discriminated schizophrenics from other subjects in a prospective follow-up and family study of 500 psychiatric outpatients. Four symptoms tended to occur together as a stable syndrome throughout the six- to 12-year follow-up: persecutory delusions, delusions of control, firmly fixed mood-incongruent delusions, and auditory hallucinations. Scale scores were computed as the number of these four symptoms that was present less one if there was a history of spending sprees with marked elation. More than 68% of the schizophrenics and fewer than 2% of nonschizophrenics had scores of +2 or greater. The distribution of scores was bimodal: persons with scores of +1 were relatively rare. Also, there was familial resemblance for the presence or absence of schizophrenia, but no additional resemblance for the number of schizophrenic symptoms. Despite this relative discreteness, scale scores were valuable for quantifying the certainty of diagnosis and predicting outcome.
Cloninger CR, Martin RL, Guze SB, Clayton PJ. Diagnosis and Prognosis in Schizophrenia. Arch Gen Psychiatry. 1985;42(1):15-25. doi:10.1001/archpsyc.1985.01790240017002