Background: Most studies reporting the gender difference in age at onset of schizophrenia show an earlier onset in males, but vary considerably in their estimates of the difference. This may be due to variations in study design, setting and diagnostic criteria. In particular, several studies conducted in developing countries have found no difference or a reversed effect whereby females have an earlier onset. The aim of the study was to investigate gender differences in age of onset, and the impact of study design and setting on estimates thereof.
Method: Study methods were a systematic literature search, meta-analysis and meta-regression.
Results: A total of 46 studies with 29,218 males and 19,402 females fulfilled the inclusion criteria and were entered into a meta-analysis. A random-effects model gave a pooled estimate of the gender difference of 1.07 years (95% confidence interval 0.21-1.93) for age at first admission of schizophrenia, with males having earlier onset. The gender difference in age at onset was not significantly different between developed and developing countries. Studies using diagnostic and statistical manual of mental disorders (DSM) criteria showed a significantly greater gender difference in age at onset than studies using International Classification Of Diseases (ICD) criteria, the latter showing no difference.
Conclusions: The gender difference in age of onset in schizophrenia is smaller than previously thought, and appears absent in studies using ICD. There is no evidence that the gender difference differs between developed and developing countries.