Risk factors in schizophrenia: season birth in Maryland, USA.

The association between the risk for schizophrenia and season of birth was studied using a standard actuarial life table method. This method of analysis eliminates the possibility of the previously described statistical artifacts from the data. An increased risk for schizophrenia for winter born individuals was demonstrated. The analysis also supported the hypothesis that season of birth is associated with an increased risk for a subtype of schizophrenia.