Urbanicity

The risk of psychotic disorder in the population exposed to urbanicity alone was 1.59% (31/1946), the risk in those exposed to family history, broadly defined, alone was 3.01% ... Thus, between 60% and 70% of the individuals exposed to both urbanicity and family history had developed psychotic disorder because of the synergistic action of the two proxy causes.

To assess this hypothesis, the urbanicity of a boy's place of residence was run against enlistment.

2002: Heinz Häfner (ed), Risk and Protective Factors in Schizophrenia: Towards a Conceptual Model of the Disease Process A number of studies have associated urbanicity at birth or upbringing with schizophrenia risk.