Is the earlier age at onset of schizophrenia in males a confounded finding

Background The finding of an earlier age at onset of schizophrenia in males compared with females, replicated across a number of studies, appears to be so robust as to support hypotheses about gender differences in the aetiology of the disorder. However, the possibility that this observed gender effect might reflect other confounding variables has not been adequately explored.Method We analysed data on 778 men and 653 women, in three developing countries and in seven developed countries, who had been assessed in the WHO 10-country study of schizophrenia. We applied a generalised linear modelling strategy to estimate the unconfounded contributions of gender, family history, premorbid personality and marital status to age at onset.Results The model that explained the highest percentage of the total variance indicated strong main effects (P