If an event like the Dutch Hunger Winter caused a unique and dramatic decline in population fertility that differentially affected the social classes, confounding by socioeconomic status must be ruled out before conclusions can be drawn about a possible association between prenatal nutritional deficiency and later schizophrenia, as suggested by Susser et al.1 The exposed (EX2) cohort was marked by a 50% decline in fertility. This decrease was associated with socioeconomic status, because it particularly affected the class of manual occupations.2 The authors state that "no relation has been found in the Netherlands between schizophrenia and low social class of origin." The question, however, is whether the outcome under investigation (discharge from a psychiatric hospital with a diagnosis of schizophrenia in the Netherlands) is possibly associated with higher socioeconomic status of origin, because only this would lead to a spurious association. In fact, the well-known Dutch study3
van Os J. Schizophrenia After Prenatal Famine. Arch Gen Psychiatry. 1997;54(6):577–578. doi:10.1001/archpsyc.1997.01830180095015
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