Why factors rooted in the family may solely explain the urban-rural differences in schizophrenia risk estimates

Many studies have identified urban-rural differences in schizophrenia risk. The underlying cause(s) may hypothetically include toxic exposures, diet, infections, and selective migration. In a recent study, we concluded that some of the cause(s) responsible for the urban-rural differences in schizophrenia risk are rooted in families, but some might also be rooted in individuals. First, we describe temporality as a potential methodological pitfall within this line of research, then we review studies not subject to this pitfall, and finally, we describe why factors rooted in the family may solely explain the urban-rural differences. Although other potential explanations for these differences exist, we focus on this hypothesis as it has not previously been discussed in detail. To determine the cause(s) responsible for the urban-rural differences, we need direct measurements of genetic and/or environmental factors related to urban life.