Is age of onset in schizophrenia influenced by marital status? Some remarks on the difficulties and pitfalls in the systematic testing of a "simple" question.

Schizophrenia is a disease characterized by a distinctly higher age at onset and at first admission in females than in males. In a systematic study on gender differences in schizophrenia we have confirmed this finding using different sets of data, in particular through the examination of a large and representative sample of first-admitted patients. The question addressed in this paper is whether marital status influences this sex-specific age difference. Assuming that marriage or a stable relationship is a protective factor in schizophrenia, delaying the onset of the disease or first hospitalization, the hypothesis was formulated that the later age of onset in women is at least partly explained by their generally earlier age of marriage. Testing this hypothesis illustrates some of the methodological problems that often occur when a causal analysis of social data is attempted. The problems emerge especially when both the dependent variable (age of onset/first admission) and the independent variable (marital status) are essentially related to age. First results appearing to indicate an influence of marital status on age at first admission did not bear a critical interpretation.