Birth Seasonality and Schizophrenia

To the Editor.—  I believe that the data presented by Watson et al¹ indicate that there is no causal relationship between the incidence of infectious diseases and increased winter births among schizophrenics. This is, of course, the opposite of what Watson et al hint that their data suggest, ie, a "prenatal rather than postnatal effect."The authors examined the effects of winter and summer infectious diseases on the elevated winter birthrates for schizophrenics. Looking at the data for all schizophrenics, there is no statistically significant increase in the number of winter-born schizophrenics during high-incidence "winter disease" years. High summer disease rates seem to protect against schizophrenia, since there is a decline in the number of winter-born schizophrenics in high-incidence summer disease years! In fact, this 5.8% decline was the largest change among the 32 pairs given in the top section of their Table and was the only one to achieve