Advancing the study of local ethnic density and psychosis
Authors: Deidre M Anglin
Journal: The Lancet Psychiatry (2020)

Most studies of neighbourhood ethnic density and psychosis have used cross-sectional data to explore the association between the two. Specifically, evidence predominantly emanating from European countries (eg, the UK, the Netherlands) has supported the ethnic density hypothesis—namely, that living in a neighbourhood with a lower proportion of one's own ethnic group is associated with a higher risk of psychosis.1Kirkbride JB Morgan C Fearon P Dazzan P Murray RM Jones PB Neighbourhood-level effects on psychoses: re-examining the role of context.Psychol Med. 2007; 37: 1413-1425Crossref PubMed Scopus (142) Google Scholar, 2Veling W Susser E Van Os J Mackenbach JP Selten JP Hoek HW Ethnic density of neighborhoods and incidence of psychotic disorders among immigrants.Am J Psychiatry. 2008; 165: 66-73Crossref PubMed Scopus (249) Google Scholar Findings from studies that ascertain neighbourhood ethnic density at or near illness onset are vulnerable to interpretations of social drift across neighbourhoods over time.3March D Hatch SL Morgan C et al.Psychosis and place.Epidemiol Rev. 2008; 30: 84-100Crossref PubMed Scopus (201) Google Scholar Those at higher risk of psychosis might have accrued such risks during childhood in ethnically dense areas, only later drifting to more socially isolated neighbourhood areas due to the ramifications of illness. This is especially a concern since other outcomes, such as depression and anxiety, which are less vulnerable to social selection processes, show weaker and less consistent associations with neighbourhood ethnic density.4Bécares L Dewey ME Das-Munshi J Ethnic density effects for adult mental health: systematic review and meta-analysis of international studies.Psychol Med. 2017; 48: 2054-2072Crossref PubMed Scopus (43) Google Scholar While researchers using a Danish registry5Schofield P Thygesen M Das-Munshi J et al.Ethnic density, urbanicity and psychosis risk for migrant groups—a population cohort study.Schizophr Res. 2017; 190: 82-87Crossref PubMed Scopus (36) Google Scholar were the first to address this vulnerability by supporting the ethnic density hypothesis longitudinally, the study by Jennifer Dykxhoorn and colleagues6Dykxhoorn J Lewis G Hollander A-C Kirkbride JB Dalman C Association of neighbourhood migrant density and risk of non-affective psychosis: a national, longitudinal cohort study.Lancet Psychiatry. 2020; (published online March 5.)https://doi.org/10.1016/S2215-0366(20)30059-6Summary Full Text Full Text PDF PubMed Scopus (16) Google Scholar published in The Lancet Psychiatry is the first to do this while differentiating first-generation from second-generation migrant density and probable visible minority status from probable non-visible minority status. A large prospective Swedish population registry captured the neighbourhood ethnic density of 468 223 migrants and their children at age 15 years, or when migration to Sweden occurred if later than 15 years of age. This cohort was tracked until emigration, death, or study end (Dec 31, 2016) for the outcome of a an ICD-10 diagnosis of non-affective psychosis (F20–29). In addition to replicating the ethnic density finding (ie, a 5% decrease in own-region migrant density corresponded to a 3% increase in psychosis risk), which got stronger after controlling for known neighbourhood-level confounders such as deprivation and population density and individual-level factors such as familial socioeconomic indicators (hazard ratio 1·05 [95% CI 1·03–1·06]), they found increased risk in both migrants and children of migrants. This study also showed that, for migrants, reduced generation-specific own-group migrant density was associated with risk of psychosis (hazard ratio 1·07 [1·04–1·11] per 5% decrease in density). Living day to day among other first-generation migrants from the region of origin could be particularly important given migrants are generally less acculturated to the new society than the second generation. Generation-specific density is likely to affect the degree to which one can find others who speak the same language, have a strong cultural identity, and share memories of home. This reveals possible protective cultural factors for psychosis risk. A high degree of generation-specific ethnic density might even be a protective factor for migrants in other regions of the world, as several US-based studies have found migrants to have better mental health than their US-born children and non-migrants.7Marks AK Ejesi K García Coll C Understanding the US immigrant paradox in childhood and adolescence.Child Dev Perspect. 2014; 8: 59-64Crossref Scopus (164) Google Scholar This possibility should be examined in future studies of immigration and health. This study's contribution also lies in the power to disentangle crucial factors often conflated in neighbourhood ethnic density studies—ie, region of origin, generational status, and visibility of migrant minority status. Dykxhoorn and colleagues6Dykxhoorn J Lewis G Hollander A-C Kirkbride JB Dalman C Association of neighbourhood migrant density and risk of non-affective psychosis: a national, longitudinal cohort study.Lancet Psychiatry. 2020; (published online March 5.)https://doi.org/10.1016/S2215-0366(20)30059-6Summary Full Text Full Text PDF PubMed Scopus (16) Google Scholar differentiated migrants who are "probable visible minority"—ie, likely to be visibly different from the white majority of the country—by combining those coming from Asia, the Middle East, north Africa, sub-Saharan Africa, and South America. This operationalisation of "visible minority status" is quite imprecise, lumping together several very different regions with different cultures and historical relationships to Sweden. But demarcations of what constitutes a group unit should be driven by what is historically meaningful in the social hierarchical structure of a given society. Within this Swedish context, for migrants with probable visible minority status, a 5% decrease in own-region neighbourhood ethnic density was associated with a 7% increase in psychosis risk, whereas for non-visible migrants and for children of migrants, there was no elevated risk. Migrants, particularly from sub-Saharan African and Asian regions, are visible minorities even among the migrant population of Sweden, as the largest proportion of migrants was of European origin (32%). This compounding minority status could be particularly isolating in a neighbourhood with low own-region ethnic density and could exacerbate the degree of social othering and prejudice experienced by such groups—othering from other migrants as well as the larger Swedish majority. Racial discrimination is an important social stressor implicated in psychosis risk8Anglin DM Lighty Q Greenspoon M Ellman LM Racial discrimination is associated with distressing subthreshold positive psychotic symptoms among US urban ethnic minority young adults.Soc Psychiatry Psychiatr Epidemiol. 2014; 49: 1545-1555Crossref PubMed Scopus (45) Google Scholar that could be exacerbated in neighbourhood contexts with low ethnic density.9Bécares L Nazroo J Stafford M The buffering effects of ethnic density on experienced racism and health.Health Place. 2009; 15: 700-708Crossref Scopus (218) Google Scholar How many residents and how much block coverage are necessary to experience a neighbourhood as high or low in own-group density? For Dykxhoorn and colleagues,6Dykxhoorn J Lewis G Hollander A-C Kirkbride JB Dalman C Association of neighbourhood migrant density and risk of non-affective psychosis: a national, longitudinal cohort study.Lancet Psychiatry. 2020; (published online March 5.)https://doi.org/10.1016/S2215-0366(20)30059-6Summary Full Text Full Text PDF PubMed Scopus (16) Google Scholar the neighbourhood unit, with a median population size of 726 people (IQR 312–1378), was smaller than in some previous studies,5Schofield P Thygesen M Das-Munshi J et al.Ethnic density, urbanicity and psychosis risk for migrant groups—a population cohort study.Schizophr Res. 2017; 190: 82-87Crossref PubMed Scopus (36) Google Scholar which might have contributed to their ability to detect the migrant density effect for migrants and their children. Work from Anglin and colleagues10Anglin DM Lui F Schneider M Ellman LM Changes in perceived neighborhood ethnic density among racial and ethnic minorities over time and psychotic-like experiences.Schizophr Res. 2019; (published online Dec 9.)DOI:10.1016/j.schres.2019.11.034Crossref PubMed Scopus (8) Google Scholar suggests that understanding neighbourhood ethnic density from the perspective of residents might be a valuable way to circumvent the challenge of determining spatially how much neighbourhood is meaningful. Future studies should incorporate both objective and subjective indicators of neighbourhood ethnic density and context. Despite not incorporating this subjective perspective of residents, Dykxhoorn and colleagues' large cohort study represents an important advancement in the field of social epidemiology, bringing us closer to unpacking how the social environment increases risk for psychosis. I declare no competing interests. Association of neighbourhood migrant density and risk of non-affective psychosis: a national, longitudinal cohort studyMigrant density was associated with non-affective psychosis risk in migrants and their children. Stronger protective effects of migrant density were found for probable visible minority migrants and migrants from Asia and sub-Saharan Africa. For migrants, this risk intersected with generation status. Together, these results suggest that this health inequality is socially constructed. Full-Text PDF Open Access