Variation of subclinical psychosis as a function of population density across different European settings: Findings from the multi-national EU-GEI study.

Background: Urbanicity is a well-established risk factor for psychosis. Our recent multi-national study found an association between urbanicity and clinical psychosis in Northern Europe but not in Southern Europe. In this study, we hypothesized that the effect of current urbanicity on variation of schizotypy would be greater in North-western Europe countries than in Southern Europe ones.

Methods: We recruited 1080 individuals representative of the populations aged 18-64 of 14 different sites within 5 countries, classified as either North-western Europe (England, France, and The Netherlands) with Southern Europe (Spain and Italy). Our main outcome was schizotypy, assessed through the Structured Interview for Schizotypy-Revised. Our main exposure was current urbanicity, operationalized as local population density. A priori confounders were age, sex, ethnic minority status, childhood maltreatment, and social capital. Schizotypy variation was assessed using multi-level regression analysis. To test the differential effect of urbanicity between North-western and Southern European, we added an interaction term between population density and region of recruitment.

Results: Population density was associated with schizotypy (β = 0.248,95%CI = 0.122-0.375;p < 0.001). The addition of the interaction term improved the model fit (likelihood test ratio:χ  = 6.85; p = 0.009). The effect of urbanicity on schizotypy was substantially stronger in North-western Europe (β = 0.620,95%CI = 0.362-0.877;p < 0.001) compared with Southern Europe (β = 0.190,95%CI = 0.083-0.297;p = 0.001).

Conclusions: The association between urbanicity and both subclinical schizotypy and clinical psychosis, rather than being universal, is context-specific. Considering that urbanization is a rapid and global process, further research is needed to disentangle the specific factors underlying this relationship.