This study compares the school-record data of 29 schizophrenics, their siblings, and controls. It relates the school-record data for each proband with his age at first psychiatric hospitalization and the amount of time subsequently accumulated in institutions for the mentally ill. School failure in childhood does not distinguish preschizophrenics from controls but, within the preschizophrenic group, repeating probands differ from nonrepeating probands on several important measures. Since the two groups differ in the course of their schizophrenic illness, they may also differ in etiologic factors. The most striking result is that schizophrenics with low childhood IQs show an earlier onset and remain institutionalized significantly longer than schizophrenics with average IQs. The strength of the relationship between IQ and prognosis in schizophrenic illness has not been fully appreciated in the past.
Offord DR, Cross LA. Adult Schizophrenia With Scholastic Failure or Low IQ in ChildhoodA Preliminary Report. Arch Gen Psychiatry. 1971;24(5):431-436. doi:10.1001/archpsyc.1971.01750110043007