Birth order sibship size and socio-economic factors in risk of schizophrenia in Greece.

A case-control study was undertaken to evaluate the effects, if any, of sibship size, birth order and parents' age at birth on the risk of a person's developing schizophrenia. Information was obtained, during an 18-month period, from 221 schizophrenic patients in the only mental-health hospital of the region of Peloponese, Greece, and from an equal number of matched patients. The data were analysed by modelling through logistic regression. No relationship was found between the occurrence of schizophrenia in a patient and either father's or mother's age at patient's birth, or sibship size, or birth order, when demographic and socio-economic variables were accounted for in the analysis. Although patients with schizophrenia were of similar socio-economic status to the comparison patients, they came from families with higher original socio-economic status, a fact which appears to reflect the decline of both schizophrenic and pre-schizophrenic people in the social ladder.