Neighbourhood variation in incidence of schizophrenia Evidence for person-environment interaction

Background Neighbourhood characteristics may influence the risk of psychosis, independently of their individual-level equivalents. Aims To examine these issues in a multi-level model of schizophrenia incidence. Method Cases of schizophrenia, incident between 1986 and 1997, were identified from the Maastricht Mental Health Case Register. A multi-level analysis was conducted to examine the independent effects of individual-level and neighbourhood-level variables in 35 neighbourhoods. Results Independent of individual-level single and divorced marital status, an effect of the proportion of single persons and proportion of divorced persons in a neighbourhood was apparent (per 1% increase respectively: RR=1.02; 95% CI 1.00-1.03; and RR=1.12, 95% CI 1.04-1.21). Single marital status interacted with the neighbourhood proportion of single persons, the effect being stronger in neighbourhoods with fewer single-person households. Conclusions The neighbourhood environment modifies the individual risk for schizophrenia. Premorbid vulnerability resulting in single marital status may be more likely to progress to over disease in an environment with a higher perceived level of social isolation.