Soc Psychiatry Psychiatr Epidemiol DOI 10.1007/s00127-014-0842-z
ORIGINAL PAPER
Neighborhood ethnic density and psychotic disorders among ethnic minority groups in Utrecht City Fabian Termorshuizen • Hugo M. Smeets Arjan W. Braam • Wim Veling
•
Received: 9 October 2013 / Accepted: 3 February 2014 Ó Springer-Verlag Berlin Heidelberg 2014
Abstract Purpose Recent studies have shown increased incidence of non-affective psychotic disorders (NAPD) among ethnic minorities compared to the native population, but not, or less so, in areas with a high own-group proportion. The aim is to investigate this ethnic density effect in Utrecht and whether this effect is due to higher rates of NAPD among Dutch persons in areas with high minority proportions. We also explore the geographical scale at which this effect occurs and the influence of social drift prior to NAPD. Methods NAPD cases in the Psychiatric Case Registry Middle Netherlands (N = 2,064) and living in Utrecht
Electronic supplementary material The online version of this article (doi:10.1007/s00127-014-0842-z) contains supplementary material, which is available to authorized users. F. Termorshuizen (&) H. M. Smeets Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, PO Box 85500, 3508 GA Utrecht, The Netherlands e-mail: [email protected] H. M. Smeets Achmea Health Insurance, PO Box 1725, 3800 BS Amersfoort, The Netherlands A. W. Braam Department of Emergency Psychiatry and Department of Specialist Training, Altrecht Mental Health Care, Lange Nieuwstraat 119, 3512 PG Utrecht, The Netherlands W. Veling Parnassia Group, Center for Early Psychosis, Lijnbaan 4, 2512 VA Den Haag, The Netherlands W. Veling Department of Psychiatry, University of Groningen, PO Box 30.001, 9700 RB Groningen, The Netherlands
during 2000–2009 were analyzed in a Poisson model in relation to both individual-level and district- vs. neighborhood-level characteristics. Results With increasing minority density, especially of the neighborhood, the rate ratios of NAPD significantly decreased among both non-Western (from 2.36 to 1.24) and Western immigrants (from 1.63 to 1.01), in comparison with Dutch persons. This was partly explained by higher rates of NAPD among Dutch persons in areas with high minority density. But there was also a trend to lower NAPD rates among non-Western minorities in these areas (P = 0.074).This trend was significant among Surinamese/ Antilleans (P = 0.001) and Moroccans aged 18–30 years (P = 0.046). Among the Dutch, a social drift to minoritydense neighborhoods prior to NAPD registration was found. Conclusions Our findings support the beneficial association with own-group presence at the smaller scale neighborhood level. Findings show also that this association is more pronounced in immigrant vs. native comparisons and is not found within all ethnic groups. Keywords Psychosis Ethnic minority density Neighborhood Psychiatric case registry Social drift
Introduction In many countries, the incidence rates of non-affective psychotic disorders (NAPD) are higher in ethnic minorities than in majority populations [1, 2]. A recent systematic review, including four multilevel studies from the UK [3– 6] and one from the Netherlands [7], showed that the relative risk of NAPD is increased among ethnic minorities living in areas with few people of the same ethnicity, but
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not, or much less so, in areas with a high proportion of ethnic minorities [8]. It remains unclear on what geographical scale the ethnic density effect operates, and whether it applies to all ethnic minority groups in an area. Also, most studies did not examine the possibility that a low relative risk among ethnic minorities in high owngroup density areas may reflect higher incidence rates in the majority population in these areas rather than lower rates in ethnic minorities. The study of Schofield et al. [6] reported incidence rates across quintiles of ethnic density within the black population in South East London and found a protective within-ethnic group density association. Previous studies typically examined associations between psychosis and neighborhood ethnic density at the time of first contact with health services. Since individuals in the early stages of psychotic illness tend to withdraw themselves from social contact and may have a downward shift in socioeconomic status as a result of poorer social functioning (‘social drift’), they may move to other neighborhoods prior to first contact with health services. It should be examined whether moving to a lower (for ethnic minorities) or to a higher minority-dense area (for the majority population) prior to the registration of NAPD diagnosis might explain the observed density effect as an artifact of reverse causation. In the present study, the association between ethnic density and rates of registered NAPD was investigated in separate ethnic minority populations and in the majority Dutch population in Utrecht City, the Netherlands. Two geographical scales for ethnic density were used (district and neighborhood), and the possible influence of moving house to an area with a lower or higher own-group density on the results was examined.
for that person but his/her historical records are retained and available for analysis. Patients and data extraction The data of all patients with a diagnosis of NAPD (DSM-IV codes 295.xx, 297.xx, 298.xx, and 293.xx) were extracted. Those patients were selected for the analysis with the earliest registration in the PCR-MN during the period January 2000 until December 2009. The PCR-MN became operational in 1999. The selection of diagnoses from 2000 onward was done to include a higher proportion of cases that were treatment incident. These cases were linked to the population registry. The staff of the CBS performed this linkage, using information on the patient’s date of birth, gender and part of the postal code. Dutch privacy law allows the use of personal (healthcare) data on behalf of scientific research, provided that the analysis results cannot be traced to a unique person. For that reason, to ensure anonymity, the staff of CBS have removed the postal code and date of birth from the analysis files. For about 80 % of the patients, a unique match with the population registry could be established. This percentage was also found in other studies of PCR-MN [10, 11] and is a characteristic of the linkage procedure when using the above-mentioned variables for personal identification. To estimate NAPD rates and rate ratios, the records of all inhabitants of Utrecht City in the period 2000–2009, aged 18 years and over, were used to calculate the number of person years of observation for the denominator. As the analysis was restricted to Utrecht City and this age category, only those NAPD patients who resided in Utrecht City during (at least a part of) the years 2000–2009 and aged 18 years and over during (at least a part of) this period were included. Definition of ethnic origin and ethnic density
Methods Databases A retrospective cohort study was performed using data from (a) the Psychiatric Case Register Middle Netherlands (PCR-MN) and (b) the population registry of Statistics Netherlands (in Dutch: ‘Centraal Bureau voor de Statistiek’, CBS). In the PCR-MN, the diagnoses of in- and outpatients of all psychiatric services and related healthcare consumption in Utrecht City (about 300,000 inhabitants) and surroundings are registered since 1999 [9]. In the population register of the CBS, all legally residing citizens of the Netherlands are registered with date of birth, gender, country of birth, country of birth of each parent, place of residence and neighborhood, and date of death. When a person is changing place of abode, a new record is added
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According to the CBS definition of immigrant status, the country of birth of the person and his/her parents was used to classify ethnic origin. A Dutch-born subject with two Dutch-born parents was considered native Dutch. A Dutch-born subject with at least one foreign-born parent was classified according to the country of birth of that parent. When the parents were born in different foreign countries, the maternal country of birth was decisive for assignment to a particular group. Most ethnic minorities in the study area originated from Turkey, Morocco, Surinam and the Netherlands Antilles. The latter two groups of migrants from former Dutch colonies with relative geographical proximity were collapsed into a single group in the analyses. Other ethnic minorities were categorized in non-Western (from countries with developing economies) and Western (including both
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countries with developed and countries with transition economies) origin. Utrecht City is divided into ten districts. Each district encloses on average about ten neighborhoods (see ‘‘Appendix: Table 5’’). Within each district and within each neighborhood separately (N = 98), the percentage of observation time during 2000–2009 related to a specific ethnic minority group was calculated. For each ethnic group, the selected individual records of the population register were aggregated during these years by district and neighborhood. This was done after weighting by the registered time living in the district and the neighborhood, respectively. The calculated percentages were regarded as measure for own-group minority ethnic density at district and neighborhood level during the study period. These percentages were each highly correlated (r ranged from 0.91 to 0.99) with the proportion of inhabitants with that specific ethnic origin in a certain district and in a certain neighborhood, respectively, on January 1, 2005. The average ethnic density related to all persons from non-Dutch origin was 29.9 % on district level, ranging from districts with 16.4 % to districts with 48.8 %. On a neighborhood level, a similar mean (26.8 %) but a much wider range was found (2.9–82.8 %) (see ‘‘Appendix: Table 5’’). Analysis Cohort study The NAPD rates were analyzed by ethnic density, which was calculated first on district and next on neighborhood level. This was done to find out whether analyzing on a more fine-grained geographical level might lead to different results [6]. Each NAPD case was assigned to the district and neighborhood in Utrecht where he/she was living at the time of first registration of the diagnosis in the PCR-MN. Separate multilevel multivariable Poisson models were designed for the comparison of the NAPD rate among (1) non-Dutch Western persons with the NAPD rate among native Dutch persons and (2) among all non-Western persons with that among native Dutch persons, and so on for (3) Turkish, (4) Moroccan, (5) Surinamese/Antillean, and (6) other non-Western persons. These comparisons were done for different values of the own-group minority density. Thus, for each minority group defined in this manner, district-level and neighborhood-level values for own-group minority density were included in the models. In the analyses with ethnic density on district level, the individual person was the first level and the district was the second level. In the analyses with ethnic density on neighborhood level, the individual person was again the first level and neighborhood was the second level of clustering. As the effect of ethnic origin as first-level characteristic on
psychosis rate may depend on ethnic density of the area of residence as-second level characteristic, the ethnic density hypothesis was tested by inclusion of terms for cross-level interaction of (ethnic origin 9 ethnic density), as was done in earlier studies [3–7]. Ethnic density was included as a measure categorized in tertiles and as continuous measure in two separate models. Age, gender, and ethnic origin were included as individual-level covariates, and minority density was included as district/neighborhood-level covariate. The neighborhood-level analyses were also adjusted for mean income of the neighborhood to find out whether differences in socioeconomic status (SES) might explain the association between ethnic density and NAPD rates. The number of districts (N = 10) was too small to include an additional second-level covariate. A decrease of the rate ratio (RR) of NAPD among those belonging to an ethnic minority compared to native Dutch persons with increasing minority ethnic density was hypothesized. This decrease may be the result of either a decreasing NAPD rate among those of foreign origin or an increasing rate among the native Dutch (or both). The Poisson model makes it possible to disentangle the between-group and within-group effects of minority density underlying such an interaction effect. All analyses were repeated (1) with restriction to the observation time and NAPD cases among those aged 18–30 years and (2) the observation time and cases registered in 2005–2009. These sensitivity analyses were done to explore whether the results were sensitive to restriction to a sample of cases that were more likely to be treatment incident and necessarily have a short illness duration at the time of earliest registration of the NAPD diagnosis in the PCR-MN. The nested case–control study To find out whether differences in rates of moving house prior to registration of NAPD from high- to low- or low- to high-density setting might explain the observed ethnic density effect, a nested case–control study was performed. NAPD cases with an earliest registered diagnosis in 2005–2009 (N = 1,073) were selected. For each case, four control persons without NAPD were randomly selected from the whole population cohort, matched by gender, year of birth, ethnic origin and ethnic density of the neighborhood of residence at the time of NAPD registration of the patient (N = 4,178). It was assessed whether the patient and the matched controls moved house from a setting with a lower to a setting with a higher ethnic minority density (as measured in tertiles) and/or in the reverse direction during the 5 years prior to the patients’ date of earliest NAPD registration (the ‘index date’). Differences in percentages between cases and controls with at least one such
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Soc Psychiatry Psychiatr Epidemiol Table 1 Demographic characteristics of sample and denominator population NAPD N (%)
Unique persons N/person years N (%)
2,064 (100 %)
404,595/2,241,320 (100)
1,180 (57.2 %) 884 (42.8 %)
191,785/1,065,099 (47.5) 212,810/1,176,221 (52.5)
18–30
506 (24.5)
213,230/684,690.5 (30.5)
30–40
539 (26.1)
141,686/536,110.7 (23.9)
40–60
697 (33.8)
113,519/619,226.0 (27.6)
[60
322 (15.6)
66,921/401,293.0 (17.9)
1,242 (60.2 %)
284,747/1,625,469 (72.5)
Total Gender Male Female Age (years)
Ethnicity Dutch
Results Description
Other Western
237 (11.5 %)
52,765/239,064 (10.7)
Turkish
81 (3.9 %)
12,309/80,691 (3.6)
Moroccan
222 (10.8 %)
21,409/144,999 (6.5)
Surinamese/Antillean
155 (7.5 %)
13,404/71,653 (3.2)
Other non-Western
127 (6.2 %)
20,230/79,444 (3.5)
Year of diagnosis 2000–2002 2003–2005
603 (29.2 %) 605 (29.3 %)
2006–2007
469 (22.7 %)
2008–2009
387 (18.8 %)
Subdiagnosis of NAPD Schizophreniaa
928 (45.0 %)
Schizophreniformb/Affectivec/delusional disorderd
346 (16.8 %)
Psychotic disorder othere or NOSf
790 (38.3 %)
NAPD non-affective psychotic disorders a
DSM-IV codes 295.20, 295.10, 295.30, 295.60, 295.90
b
295.40
c
295.70
d
297.1
e
298.80, 297.30, 293.81, 293.82
f
298.90
transition were assessed for all ethnic groups separately and tested in a logistic regression model. It was hypothesized that NAPD cases of Dutch origin more often moved to a neighborhood with a lower SES during the prodromal or early stages of NAPD (‘social drift’). As these neighborhoods are most often also characterized by high ethnic minority density, this might (partly) explain the (possible) trend toward lower RR among ethnic minorities compared to the Dutch in high-density areas. For ethnic minorities, a drift to areas with similar or lower SES, but with lower
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own-group minority density during the prodromal or early stages of NAPD might theoretically explain a density effect as well. However, this seems less obvious, if not impossible. Ordinary logistic regression was used with and without adjustment for the matching factors. Data-management, record linking, the sampling of controls, and logistic regression were performed with SPPS, version 14.0. The multilevel Poisson regression analysis was performed with STATA, version 11.0, using procedure GLAMM [12].
The population of Utrecht City in the period 2000–2009 consisted of 404,595 (whole period) unique persons aged 18 years and older, who contributed with 2,241,320 person years of observation to the present analysis. Among these persons and during these years, 2,064 cases of NAPD were registered in the PCR-MN during 2000–2009. The mean age at earliest registration of diagnosis in the PCR-MN was 43.0 years. In Table 1, the characteristics of these cases and the source population are given. Non-Western and Western minorities compared to native Dutch The adjusted RR of NAPD among non-Western compared to Dutch persons decreased from 2.26 in districts with low nonWestern minority density (\21.2 %) to 1.51 in districts with high non-Western density (C38.4 %). This resulted in statistically significant terms for (ethnic density 9 ethnic origin) interaction (P = 0.016 when using a categorized measure, and P = 0.001 when using a continuous measure for ethnic density) (Table 2). This interaction appeared to be the result of slightly higher NAPD rates among Dutch persons (RR = 1.39, NS) and slightly lower NAPD rates among non-Western persons (RR = 0.93, NS) in districts with high non-Western minority density compared to districts with low density. When analyzing the data on a neighborhood level, similar but more pronounced results were found. Again, the RRs of NAPD among non-Western persons compared to native Dutch persons clearly decreased with increasing ethnic density. Without adjustment for mean income as neighborhood-level covariate, the NAPD rates among the Dutch majority population significantly increased with higher non-Western minority density (RR = 1.31 and 1.49, P \ 0.05). After adjustment for mean income of the neighborhood, this increasing trend became substantially less strong (P = 0.067). The NAPD rates among the non-Western minorities, on the other hand, showed more pronounced
Soc Psychiatry Psychiatr Epidemiol Table 2 Rate ratios (RRs) of NAPD among non-Western minorities compared to the Dutch by district/neighborhood ethnic density (‘between groups’) and among high-density districts/neighborhoods compared to low-density districts/neighborhoods by ethnic group (‘within’) Between groups: RR of NAPD non-Dutch vs. Dutch (=#ref)
Within ‘Dutch’: RR of NAPD high vs. low density
Within ‘non-Dutch’: RR of NAPD high vs. low density
All non-Western minorities Without adjustment for SES Ethnic density–district (N of Dutch/N of non-Dutch cases) \21.2 % (N = 626/167) 2.26 [1.84–2.79] 21.2–38.4 % (N = 335/180) C38.4 % (N = 281/238)
2.02 [1.65–2.47]
1.00 (=#ref)
1.00 (=#ref)
0.97 [0.61–1.57]
0.87 [0.48–1.57]
1.51 [1.24–1.83]
1.39 [0.84–2.32]
0.93 [0.50–1.74]
Ix: P = 0.016 (df = 2, cat.)
P = 0.254 (df = 2, cat.)
P = 0.901 (df = 2, cat.)
Ix: P = 0.001(df = 1, cont.)
P = 0.466 (df = 1, cont.)
P = 0.622(df = 1, cont.)
Ethnic density–neighborhood (N of Dutch/N of non-Dutch cases) \21.8 % (N = 827/222)
2.38 [2.03–2.79]
1.00 (= #ref)
1.00 (=#ref)
21.8–43.3 % (N = 297/197)
1.72 [1.42–2.08]
1.31 [1.01–1.71]
0.95 [0.72–1.24]
C43.3 % (N = 118/166)
1.24 [0.96–1.61]
1.49 [0.99–2.25]
0.78 [0.54–1.12]
Ix: P \ 0.001 (df = 2, cat.)
P = 0.031 (df = 2, cat.)
P = 0.419 (df = 2, cat.)
Ix: P \ 0.001(df = 1,cont.)
P = 0.002 (df = 1, cont.)
P = 0.142 (df = 1, cont.)
With adjustment for SES Ethnic density–neighborhood \21.8 %
2.36 [2.02–2.76]
1.00 (= #ref)
1.00 (= #ref)
21.8–43.3 % C43.3 %
1.71 [1.41–2.07] 1.24 [0.96–1.61]
1.23 [0.93–1.62] 1.35 [0.85–2.14]
0.89 [0.67–1.18] 0.71 [0.47–1.08]
Ix: P \ 0.001 (df = 2, cat.)
P = 0.211 (df = 2, cat.)
P = 0.28 (df = 2, cat.)
Ix: P \ 0.001(df = 1,cont.)
P = 0.067 (df = 1, cont.)
P = 0.074 (df = 1, cont.)
Adjusted for age and gender SES socioeconomic status, measured as mean income of neighborhood and included as second-level covariate, Ix interaction effect of (ethnic density 9 ethnic origin), cat. ethnic density included as categorized variable, in tertiles, as shown, cont. ethnic density included as continuous variable, in %
decrease with higher non-Western minority density, reaching the level of borderline significance (P = 0.074). A similar picture of decreasing RRs of NAPD among Western minorities compared to native Dutch with higher Western minority density was found. However, this finding was fully explained by increasing NAPD rates among the Dutch with increasing Western minority density (Online supplement: Table S.1). When restricting the analyses to the observation time and NAPD cases at ages 18–30 years (506 cases in 684,690.5 person years), a similar decrease of betweengroup RRs with increasing neighborhood ethnic density was found in the analysis for non-Western minorities (P value for interaction = 0.003, continuous) (Online supplement: Table S.2). After adjustment for SES, the within-group differences were also similar in direction and magnitude, but in statistical terms less pronounced (P = 0.112 among the native Dutch, and P = 0.123 among the non-Western persons). For non-Western minorities, the analysis was also restricted to the observation time and NAPD cases in the years 2005–2009. This was done to achieve a higher proportion of incident cases,
as newly registered patients in the first 5 years of a register are likely to contain a high proportion of prevalent rather than incident cases. The effect sizes were similar in magnitude and direction, but the effect estimates for the withinnon-Western group comparison became far from statistically significant (data not shown). Separate non-Western minority groups Among all separate non-Western minorities, decreasing RRs of NAPD compared to native Dutch persons with increasing own-group density were found, resulting in significant terms for (ethnic density 9 ethnic origin) interaction (P values \0.001–0.044, continuous measure) (Table 3). Also, for these minorities in the within-group comparisons, decreasing trends of NAPD rates associated with higher own-group ethnic density were found. For the Surinamese/Antillean persons, this decreasing trend was highly significant (P = 0.001), and for non-Western persons in the category ‘other’, this trend was borderline significant (P = 0.073). When restricting the analyses to those aged 18–30 years, the trend in the between-group RRs of NAPD among the
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Soc Psychiatry Psychiatr Epidemiol Table 3 All non-Western minorities, separately for Turkish, Moroccan, Surinamese/Antillean and other non-Western minorities Between groups: RR of NAPD non-Dutch vs. Dutch (=#ref)
Within ‘Dutch’: RR of NAPD high vs. low density
Within ‘non-Dutch’: RR of NAPD high vs. low density
Turkish Ethnic density–neighborhood (N of Dutch/N of non-Dutch cases) \6.5 (N = 892/26)
1.39 [0.93–2.08]
1.00 (=#ref)
1.00 (=#ref)
6.5–9.6 % (N = 235/29)
1.19 [0.80–1.76]
1.13 [0.81–1.59]
0.97 [0.52–1.78]
C9.6 % (N = 115/26)
0.78 [0.49–1.25]
1.13 [0.71–1.78]
0.63 [0.32–1.26]
Ix: P = 0.044 (df = 1, cont.)
P = 0.336 (df = 1, cont.)
P = 0.288 (df = 1, cont.)
Moroccan Ethnic density–neighborhood (N of Dutch/N of non-Dutch cases) \11.3 % (N = 977/83)
2.18 [1.72–2.77]
1.00 (=#ref)
1.00 (= #ref)
11.3–27.6 % (N = 194/82)
1.79 [1.37–2.34]
1.25 [0.88–1.76]
1.02 [0.68–1.54]
C27.6 % (N = 71/57)
1.01 [0.70–1.47]
1.38 [0.80–2.39]
0.64 [0.37–1.10]
Ix: P \ 0.001 (df = 1, cont.)
P = 0.056 (df = 1, cont.)
P = 0.157 (df = 1, cont.)
Suriname/Antillean Ethnic density–neighborhood (N of Dutch/N of non-Dutch cases) \3.2 % (N = 676/61)
3.44 [2.61–4.53]
1.00 (= #ref)
1.00 (= #ref)
3.2–4.9 % (N = 369/57)
2.32 [1.73–3.12]
1.34 [1.03–1.75]
0.91 [0.58–1.42]
C4.9 % (N = 197/37)
2.12 [1.43–3.14]
0.83 [0.60–1.14]
0.51 [0.30–0.86]
Ix: P = 0.001 (df = 1, cont.)
P = 0.664 (df = 1, cont.)
P = 0.001 (df = 1, cont.)
Other non-Western Ethnic density–neighborhood (N of Dutch/N of non-Dutch cases) \3.5 % (N = 641/46)
2.74 [2.01–3.74]
1.00 (= #ref)
1.00 (= #ref)
3.5–6.3 % (N = 405/44) C6.3 % (N = 196/37)
2.09 [1.51–2.89] 1.35 [0.92–1.98]
1.15 [0.90–1.48] 1.37 [0.97–1.93]
0.88 [0.57–1.35] 0.67 [0.42–1.08]
Ix: P = 0.001(df = 1, cont.)
P = 0.008 (df = 1, cont.)
P = 0.073 (df = 1, cont.)
Adjusted for age, gender, and SES SES socioeconomic status, measured as mean income of neighborhood and included as second-level covariate, Ix interaction effect of (ethnic density 9 ethnic origin), cont. ethnic density included as continuous variable, in %
Turkish (from 2.32 to 0.99) and the Moroccan persons (from 4.02 to 1.79) compared to the native Dutch were more pronounced (Online supplement: Table S.2). Among the Moroccans, the within-group decrease of NAPD rates with higher own-group density was statistically significant (RR of NAPD in neighborhoods with Moroccan density of C27.6 % compared to neighborhoods with Moroccan density \11.3 % = 0.63, P = 0.046, continuous). Among the Surinamese/Antillean persons, the within-group decreasing trend disappeared. Among other non-Western persons, the results were similar to the non-restricted analysis. When restricting the analysis to the observation time and NAPD cases in the years 2005–2009, again the effect estimates were similar in magnitude and direction, but in statistical sense less pronounced (data not shown). Residential history Among Dutch NAPD patients, a significantly higher rate of moving house from a low to a high minority density (defined as % non-Dutch) neighborhood during the
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5 years prior to the index date was found, compared to Dutch controls (OR = 1.51) (Table 4). As similar results were obtained for the adjusted and non-adjusted analysis (the adjusted ORs were slightly more pronounced), the results of the univariable regression are shown. The OR of moving house from a high to a low non-Dutch ethnic density neighborhood was in the opposite direction (OR = 0.89, P = 0.486). Among ethnic minorities, no significant differences in rates of moving house from low to high or high to low own-group minority density were found, which may be caused by the small numbers and lack of power. Regardless of the statistical significance, the pattern of ORs did not fit in the hypothesis of social drift as explanation for the higher NAPD incidence among ethnic minorities in lowdensity neighborhoods. Compared to Moroccan controls, a (non-significantly) higher rate of moving house to lowdensity neighborhoods (14.0 vs. 9.7 %) and a (non-significantly) lower rate of moving house to high-density neighborhoods (6.6 vs. 11.3 %) among Moroccan NAPD patients prior to their diagnosis were found. This direction
of the ORs in itself is in accordance with the social drift hypothesis as explanation. However, for Turkish and other non-Western minorities, this pattern is fully reversed, and for the Surinamese/Antillean minority the OR of moving house to low-density areas is negligibly different from 1.00 (1.08 and a P value not far from 1.00).
P = 0.546 P = 0.828 P = 0.172
Discussion
P = 0.473 P = 0.486
P = 0.246
b a
OR = 0.47 [0.13–1.67] OR = 1.26 [0.66–2.39] OR = 0.89 [0.64–1.22]
14.9 % 7.7 %
P = 0.574
8.7 %
12.7 %
10.3 % P = 0.705 P = 0.005
7.8 % Transition from high to low minority density, %b
OR = 1.36 [0.46–4.01] OR = 1.16 [0.53–2.51] OR = 1.51 [1.13–2.03]
12.8 %
39 435
7.1 % 8.2 % 7.3 % 10.6 % Transition from low to high minority density, %a
110 2564 641 Persons, N
Cases Controls Cases
Controls
Cases
a
Defined as at least one transition between the date of NAPD diagnosis and 5 years prior to this date. See , but now transition in the opposite direction
OR = 0.77 [0.34–1.75] OR = 1.08 [0.51–2.30] OR = 1.51 [0.83–2.76]
13.0 % P = 0.289
10.4 % 14.0 %
9.7 %
11.8 %
10.9 % P = 0.704 P = 0.140
8.9 % 13.0 %
OR = 1.53 [0.69–3.35] OR = 0.87 [0.42–1.77] OR = 0.55 [0.25–1.21]
270 77
14.6 % 12.9 %
85
6.6 % 9.7 %
453 121 154
11.3 %
302
Controls Cases Controls Cases Controls
Controls
Cases
Other non-Western Surinamese/Antillean Moroccan Turkish Western Dutch
Table 4 Odds ratios (ORs) of moving house from a lower to a higher tertile and from a higher to a lower tertile of neighborhood minority density among NAPD cases compared to matched controls, by ethnic group
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This large cohort study found that the RR of registered NAPD among ethnic minorities was lower when they lived in a neighborhood with a higher proportion of people of their own ethnicity. This favorable association was stronger on neighborhood level than on district level, that is, when assessed on a smaller geographical scale. The association was found among all separate ethnic minority groups, but was in part explained by higher NAPD rates among native Dutch persons living in neighborhoods with high ethnic minority density. The higher rates among Dutch appeared to be (in part) related to social drift to these neighborhoods, as Dutch cases significantly more often had moved from low to high minority density neighborhoods prior to their date of registered NAPD diagnosis than personally matched Dutch controls in the same period. Comparison with earlier studies Our study has a unique contribution to earlier reports by clearly disentangling the between- and within-group effects of ethnic minority density. When evaluating NAPD rates within ethnic minority groups, that is, without comparison with the majority Dutch population, the density effect was found as well, albeit less pronounced and less consistently. Among Western minorities, no such effect and among nonWestern minorities a borderline significant effect on NAPD rates were found, which became more apparent and statistically significant for Surinamese/Antillean individuals and for Moroccan individuals aged \30 years. In the study of Cochrane and Bal in England, a small trend toward lower schizophrenia rates with a higher own-group density was found within the largest foreign-born groups (from the Caribbean, India, Pakistan, and Ireland), which was clear and statistically significant among Irish-born males only [13]. In the study of Halpern and Nazroo, using National Community Survey data, fewer neurotic and psychotic symptoms were reported among foreign people living in districts with high own-group concentration, but with substantial differences in size and statistical significance between different ethnic groups [14]. In this study, adjustment for economic hardship reduced the association among whites, but strengthened the association among ethnic minorities. This is in accordance with the observed
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influence of adjustment for mean neighborhood income on the estimates in our study. These findings are also consistent with the influence of downward social drift on NAPD rates in native Dutch, because high minority density neighborhoods are mostly socioeconomically more disadvantaged than low minority density neighborhoods. This also implies that the ethnic density effect among ethnic minorities cannot be explained by social drift. In our study, this conclusion is supported by the observed ethnic density effect within minority groups and the absence of increased odds of moving house to a low own-group minority density neighborhood prior to registration of NAPD. In the recent study of Jarrı´n et al. among 568 Ecuadorian migrants in Spain, contrary to expectation, an unfavorable association with high ethnic density on mental health symptom scores was found, even after adjustment for the average educational attainment of the area of residence [15]. In contrast with most other studies among wellestablished minority communities, this study was related to recently settled migrants, which suggests that the effect of ethnic density, if present, is sensitive to the context of migration history. In the multilevel studies of Kirkbride et al. in Southeast London [4, 5], of Boydell et al. in South London [3], and of Veling et al. in The Hague [7], lower RRs of psychotic disorders associated with increasing minority density were found. However, the comparison with the native majority population living in high ethnic density areas vs. the comparison across different values for area ethnic density within ethnic minority groups was not clearly disentangled. The study of Schofield et al. [6] in which general practice data on a detailed neighborhood level in South East London were analyzed, both between- and within-group effects of ethnic density on psychotic disorders among black residents were found, quite similar to our findings. Strengths and limitations The sample of NAPD cases in the present study is highly representative of patients in Utrecht who receive treatment for NAPD, as the registration of patients of psychiatric services in the Utrecht region by the PCR-MN is almost complete and a high proportion ([80 %) could be matched with a record in the population register of the CBS. Earlier analyses of data from the PCR-MN showed a somewhat lower probability for patients with a foreign origin to have a record linkage to the CBS [11]. Immigrants more often have errors in their registered birth date and illegal immigrants have no record in the population registry. A relative underrepresentation of ethnic minorities with NAPD might be expected, resulting in an underestimation of the rate ratios comparing minorities with native Dutch. This probably does not influence the found associations with ethnic
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density within ethnic groups, as an association between ethnic density of the person his/her living area and probability of record linkage seems not obvious. The population registry of the CBS is complete for all legally residing residents in the Netherlands. Thus, the full source population of the NAPD cases of Utrecht City in the study period was included in the analysis. Most important for the present study, the population register made it possible to assess the residential history of NAPD patients and their matched controls. This study has a unique contribution to earlier reports by examining for the first time whether differences in patterns of moving house prior to registration of NAPD might explain the found associations with ethnic minority density. For the potential confounding effect of SES, mean income at the district and neighborhood level was included as proxy. Adjustment for mean income at the area level is probably not sufficient to fully cover the effect of SES. Other measures such as educational attainment and prevalence of unemployment should be included as well. For ethnic minorities, however, the effect of SES probably counterbalances the effect of ethnic density, as poor mental health often predetermines an individual to live in economically disadvantaged areas, which are often also characterized by overrepresentation of ethnic minority groups. Thus, the unfavorable association with minority density among native Dutch persons after adjustment for SES (Table 2) might in part be explained by residual confounding of SES, whereas the favorable association among minorities was probably still underestimated [14]. Our results indicate that bias due to social drift is an unlikely explanation for the ethnic density effect in ethnic minorities. Even when disregarding the absence of statistical significance, the pattern of ORs did not fit in the hypothesis of social drift as explanation for the higher NAPD incidence among ethnic minorities in low-density neighborhoods. However, our analysis does not elucidate the mechanisms underlying the density effect. Data were restricted to those diagnosed in specialist psychiatric treatment. Worse access to care has been hypothesized for ethnic minorities, in particular when they are less acculturated to the host society [16]. This in turn may be associated with high ethnic density if those who are less acculturated cluster together [14]. In the Netherlands, those from ethnic minorities appear to have fairly good access to ambulatory mental health care [17]. However, differences are present with those from Moroccan origin having a lower, and those from Turkish and Antillean origin a higher, utilization of specialist mental health care [18]. Contrary to expectation, an important indicator of acculturation (communication in Dutch) appeared to be associated with lower uptake of mental health services among Moroccan subjects [19]. As differences in uptake may be
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confounded by differences in the occurrence of specific mental disorders, the issue concerning the presence of real differences in care-seeking behavior and its possible influence on the observed associations with ethnic density remains unsettled [8]. If social causation underlies the found association with ethnic density (perceived), discrimination and racism in a wider host society together with the favorable buffering effects of same-ethnic social networks and supporting communities in the direct area of residence appear to be a plausible explanation [20, 21]. Our analysis was restricted to those with a registered and, thus, a clinical diagnosis of NAPD. Our sample should be regarded as a cohort of mixed incident/prevalent nature, ignoring the time at risk between disease onset and diagnosis, and between diagnosis and registration in the PCRMN [22]. This probably explains the relatively old age of NAPD cases, on average 43.0 years, compared with other studies, e.g. 27 years in the study of Veling et al. [7], 35.4 years in the study of Boydell et al. [3], and 39.2 in the study of Schofield et al. [6]. However, density effects among non-Western minorities were also found in a selected sample of those aged \30 years, which was likely to consist of true treatment-incident cases and cases at an early stage of their illness. Our study was limited to NAPD as outcome. In earlier studies, the most consistent associations between ethnic density and mental health were found for psychotic symptoms and NAPD [8]. In few other studies, the association with ethnic density was evaluated for other disorders, such as depression and anxiety, or scores for mental health in general, but with mixed results [8]. An important outcome that might be helpful to evaluate the effect of ethnic density on mental health is risk of suicide (attempts), as suicide (attempts) may reflect a wide range of troubles, vague illness and well-defined psychiatric disorders [23]. Furthermore, our study was limited to ethnic origin as determinant of main interest. The principle of psychosocial benefit of living among persons like yourself may also be investigated for other dimensions such as sexual orientation, religion, and being long-lastingly unemployed [24].
prior to diagnosis appeared to explain (in part) these higher rates. Studies with other mental health outcome measures, but also including other psychosocial and demographic dimensions, are needed to fully evaluate the importance of living among people of their own group for the etiology and prevention of mental disorders. Acknowledgments The authors like to thank Statistics Netherlands (Centraal Bureau voor de Statistiek, CBS) for kindly providing the data necessary for the present analysis. Furthermore, the authors like to thank the participating psychiatric hospitals and services for providing all data for the Psychiatric Case Register. The authors thank Janneke Giele (Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht) for collecting the data, data management, and support in preparation of the analysis files. Structural funding of the Psychiatric Case Registers was provided by the participating psychiatric hospitals and services and by the Ministry of Health, Welfare and Sport (VWS). Representatives of the participating psychiatric hospitals and services co-decided on research priorities. The VWS had no role in the study design, analysis, and interpretation of the data, in the writing of the present report, and in the decision to submit for publication. Conflict of interest On behalf of all the authors, the corresponding author states that there is no conflict of interest.
Appendix See Table 5.
Table 5 Characteristics of districts and neighborhoods in Utrecht City Average
Range (min–max)
Districts (N = 10) Number of inhabitants 01/01/2005
27,525
12,330–40,090
Ethnic density % non-Dutch
29.9
16.4–48.8
Non-Dutch Western (%)
10.1
7.3–14.0
Non-Western (%)
19.8
7.3–40.7
Turkish (%)
4.2
0.4–10.2
Moroccan (%)
8.0
1.4–21.9
Surinamese/Antillean (%)
3.5
1.8–6.6
Other non-Western (%)
4.0
2.4–6.9
12,900 €
11,000–15,700
Mean net income per inhabitant Neighborhoods (N = 98)
Conclusion and relevance Our study contributes to the evidence that the proportion of own ethnic minority group in the direct living environment may have an important influence on the risk of psychotic disorders. When interpreting strong relative risk estimates for the effects of ethnic density, however, it must be kept in mind that these effects may be explained in part by higher rates of NAPD among natives living in areas with high minority density. Social drift to more disadvantaged areas
Number of inhabitants 01/01/2005
2,808
10–10,320
Ethnic density % non-Dutch
26.8
2.9–82.8
Non-Dutch Western (%)
10.2
2.8–39.3
Non-Western (%) Turkish (%)
16.6 3.3
0.1–77.5 0.0–21.2
Moroccan (%)
6.2
0.0–45.8
Surinamese/Antillean (%)
3.1
0.0–21.3
Other non-Western (%)
3.7
0.0–15.2
12,900 €
6,200–20,800
Mean net income per inhabitant
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References 1. Bourque F, van der Ven E, Malla A (2011) A meta-analysis of the risk for psychotic disorders among first- and second-generation immigrants. Psychol Med 41:897–910 2. Cantor-Graae E, Selten JP (2005) Schizophrenia and migration: a meta-analysis and review. Am J Psychiatry 162:12–24 3. Boydell J, van Os J, McKenzie K, Allardyce J, Goel R, McCreadie RG, Murray RM (2001) Incidence of schizophrenia in ethnic minorities in London: ecological study into interactions with environment. BMJ 323:1336–1338 4. Kirkbride JB, Morgan C, Fearon P, Dazzan P, Murray RM, Jones PB (2007) Neighbourhood-level effects on psychoses: re-examining the role of context. Psychol Med 37:1413–1425 5. Kirkbride JB, Boydell J, Ploubidis GB, Morgan C, Dazzan P, McKenzie K, Murray RM, Jones PB (2008) Testing the association between the incidence of schizophrenia and social capital in an urban area. Psychol Med 38:1083–1094 6. Schofield P, Ashworth M, Jones R (2010) Ethnic isolation and psychosis: re-examining the ethnic density effect. Psychol Med 1–7 7. Veling W, Susser E, van Os J, Mackenbach JP, Selten JP, Hoek HW (2008) Ethnic density of neighborhoods and incidence of psychotic disorders among immigrants. Am J Psychiatry 165:66–73 8. Shaw RJ, Atkin K, Becares L, Albor CB, Stafford M, Kiernan KE, Nazroo JY, Wilkinson RG, Pickett KE (2012) Impact of ethnic density on adult mental disorders: narrative review. Br J Psychiatry 201:11–19 9. Smeets HM, Laan W, Engelhard IM, Boks MP, Geerlings MI, de Wit NJ (2011) The psychiatric case register middle Netherlands. BMC Psychiatry 11:106 10. Laan W, Termorshuizen F, Smeets HM, Boks MP, de Wit NJ, Geerlings MI (2011) A comorbid anxiety disorder does not result in an excess risk of death among patients with a depressive disorder. J Affect Disord 135:284–291 11. Termorshuizen F, Wierdsma AI, Visser E, Drukker M, Sytema S, Laan W, Smeets HM, Selten JP (2012) Psychosis and suicide risk by ethnic origin and history of migration in the Netherlands. Schizophr Res 138:268–273 12. Rabe-Hesketh S, Skrondal A (2005) 6 Counts. Multilevel and longitudinal modeling using STATA, 1st edn. STATA Press, Texas, pp 181–216
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13. Cochrane R, Bal SS (1988) Ethnic density is unrelated to incidence of schizophrenia. Br J Psychiatry 153:363–366 14. Halpern D, Nazroo J (2000) The ethnic density effect: results from a national community survey of England and Wales. Int J Soc Psychiatry 46:34–46 15. Jarrin I, Garcia-Fulgueiras A, Ibanez-Rojo V, Alvarez D, GarciaPina R, Fernandez-Liria A, Garcia-Ortuzar V, Diaz D, Rodriguez-Arenas MA, Mazarrasa L, Zunzunegui MV, Llacer A, Del Amo J (2013) Absence of protective ethnic density effect on Ecuadorian migrants’ mental health in a recent migration setting: a multilevel analysis. Soc Psychiatry Psychiatr Epidemiol 48:95–103 16. Kamperman AM, Komproe IH, de Jong JT (2007) Migrant mental health: a model for indicators of mental health and health care consumption. Health Psychol 26:96–104 17. Van ‘t Land H, Grolleman J, Mutsaers K, Smits C (2008) Deel 2 Toegang en zorggebruik, Basisanalyse. In: Trendrapportage GGZ 2008. Trimbos-Instituut, Utrecht, pp 85–113 18. Uiters E, Deville WL, Foets M, Groenewegen PP (2006) Use of health care services by ethnic minorities in the Netherlands: do patterns differ? Eur J Public Health 16:388–393 19. Fassaert T, Hesselink AE, Verhoeff AP (2009) Acculturation and use of health care services by Turkish and Moroccan migrants: a cross-sectional population-based study. BMC Public Health 9:332 20. Becares L, Nazroo J, Stafford M (2009) The buffering effects of ethnic density on experienced racism and health. Health Place 15:670–678 21. Das-Munshi J, Becares L, Boydell JE, Dewey ME, Morgan C, Stansfeld SA, Prince MJ (2012) Ethnic density as a buffer for psychotic experiences: findings from a National Survey (EMPIRIC). Br J Psychiatry 201:282–290 22. Termorshuizen F, Wierdsma AI, Smeets HM, Visser E, Drukker M, Nijman H, Sytema S (2013) Cause-specific mortality among patients with psychosis: disentangling the effects of age and illness duration. Psychosomatics 54:536–545 23. Neeleman J, Wessely S (1999) Ethnic minority suicide: a small area geographical study in south London. Psychol Med 29:429–436 24. Gevonden MJ, Selten JP, Myin-Germeys I, de Graaf R, Ten Have M, van Dorsselaer S, van Os J, Veling W (2013) Sexual minority status and psychotic symptoms: findings from the Netherlands Mental Health Survey and Incidence Studies (NEMESIS). Psychol Med 1–13
ORIGINAL PAPER
Neighborhood ethnic density and psychotic disorders among ethnic minority groups in Utrecht City Fabian Termorshuizen • Hugo M. Smeets Arjan W. Braam • Wim Veling
•
Received: 9 October 2013 / Accepted: 3 February 2014 Ó Springer-Verlag Berlin Heidelberg 2014
Abstract Purpose Recent studies have shown increased incidence of non-affective psychotic disorders (NAPD) among ethnic minorities compared to the native population, but not, or less so, in areas with a high own-group proportion. The aim is to investigate this ethnic density effect in Utrecht and whether this effect is due to higher rates of NAPD among Dutch persons in areas with high minority proportions. We also explore the geographical scale at which this effect occurs and the influence of social drift prior to NAPD. Methods NAPD cases in the Psychiatric Case Registry Middle Netherlands (N = 2,064) and living in Utrecht
Electronic supplementary material The online version of this article (doi:10.1007/s00127-014-0842-z) contains supplementary material, which is available to authorized users. F. Termorshuizen (&) H. M. Smeets Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, PO Box 85500, 3508 GA Utrecht, The Netherlands e-mail: [email protected] H. M. Smeets Achmea Health Insurance, PO Box 1725, 3800 BS Amersfoort, The Netherlands A. W. Braam Department of Emergency Psychiatry and Department of Specialist Training, Altrecht Mental Health Care, Lange Nieuwstraat 119, 3512 PG Utrecht, The Netherlands W. Veling Parnassia Group, Center for Early Psychosis, Lijnbaan 4, 2512 VA Den Haag, The Netherlands W. Veling Department of Psychiatry, University of Groningen, PO Box 30.001, 9700 RB Groningen, The Netherlands
during 2000–2009 were analyzed in a Poisson model in relation to both individual-level and district- vs. neighborhood-level characteristics. Results With increasing minority density, especially of the neighborhood, the rate ratios of NAPD significantly decreased among both non-Western (from 2.36 to 1.24) and Western immigrants (from 1.63 to 1.01), in comparison with Dutch persons. This was partly explained by higher rates of NAPD among Dutch persons in areas with high minority density. But there was also a trend to lower NAPD rates among non-Western minorities in these areas (P = 0.074).This trend was significant among Surinamese/ Antilleans (P = 0.001) and Moroccans aged 18–30 years (P = 0.046). Among the Dutch, a social drift to minoritydense neighborhoods prior to NAPD registration was found. Conclusions Our findings support the beneficial association with own-group presence at the smaller scale neighborhood level. Findings show also that this association is more pronounced in immigrant vs. native comparisons and is not found within all ethnic groups. Keywords Psychosis Ethnic minority density Neighborhood Psychiatric case registry Social drift
Introduction In many countries, the incidence rates of non-affective psychotic disorders (NAPD) are higher in ethnic minorities than in majority populations [1, 2]. A recent systematic review, including four multilevel studies from the UK [3– 6] and one from the Netherlands [7], showed that the relative risk of NAPD is increased among ethnic minorities living in areas with few people of the same ethnicity, but
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not, or much less so, in areas with a high proportion of ethnic minorities [8]. It remains unclear on what geographical scale the ethnic density effect operates, and whether it applies to all ethnic minority groups in an area. Also, most studies did not examine the possibility that a low relative risk among ethnic minorities in high owngroup density areas may reflect higher incidence rates in the majority population in these areas rather than lower rates in ethnic minorities. The study of Schofield et al. [6] reported incidence rates across quintiles of ethnic density within the black population in South East London and found a protective within-ethnic group density association. Previous studies typically examined associations between psychosis and neighborhood ethnic density at the time of first contact with health services. Since individuals in the early stages of psychotic illness tend to withdraw themselves from social contact and may have a downward shift in socioeconomic status as a result of poorer social functioning (‘social drift’), they may move to other neighborhoods prior to first contact with health services. It should be examined whether moving to a lower (for ethnic minorities) or to a higher minority-dense area (for the majority population) prior to the registration of NAPD diagnosis might explain the observed density effect as an artifact of reverse causation. In the present study, the association between ethnic density and rates of registered NAPD was investigated in separate ethnic minority populations and in the majority Dutch population in Utrecht City, the Netherlands. Two geographical scales for ethnic density were used (district and neighborhood), and the possible influence of moving house to an area with a lower or higher own-group density on the results was examined.
for that person but his/her historical records are retained and available for analysis. Patients and data extraction The data of all patients with a diagnosis of NAPD (DSM-IV codes 295.xx, 297.xx, 298.xx, and 293.xx) were extracted. Those patients were selected for the analysis with the earliest registration in the PCR-MN during the period January 2000 until December 2009. The PCR-MN became operational in 1999. The selection of diagnoses from 2000 onward was done to include a higher proportion of cases that were treatment incident. These cases were linked to the population registry. The staff of the CBS performed this linkage, using information on the patient’s date of birth, gender and part of the postal code. Dutch privacy law allows the use of personal (healthcare) data on behalf of scientific research, provided that the analysis results cannot be traced to a unique person. For that reason, to ensure anonymity, the staff of CBS have removed the postal code and date of birth from the analysis files. For about 80 % of the patients, a unique match with the population registry could be established. This percentage was also found in other studies of PCR-MN [10, 11] and is a characteristic of the linkage procedure when using the above-mentioned variables for personal identification. To estimate NAPD rates and rate ratios, the records of all inhabitants of Utrecht City in the period 2000–2009, aged 18 years and over, were used to calculate the number of person years of observation for the denominator. As the analysis was restricted to Utrecht City and this age category, only those NAPD patients who resided in Utrecht City during (at least a part of) the years 2000–2009 and aged 18 years and over during (at least a part of) this period were included. Definition of ethnic origin and ethnic density
Methods Databases A retrospective cohort study was performed using data from (a) the Psychiatric Case Register Middle Netherlands (PCR-MN) and (b) the population registry of Statistics Netherlands (in Dutch: ‘Centraal Bureau voor de Statistiek’, CBS). In the PCR-MN, the diagnoses of in- and outpatients of all psychiatric services and related healthcare consumption in Utrecht City (about 300,000 inhabitants) and surroundings are registered since 1999 [9]. In the population register of the CBS, all legally residing citizens of the Netherlands are registered with date of birth, gender, country of birth, country of birth of each parent, place of residence and neighborhood, and date of death. When a person is changing place of abode, a new record is added
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According to the CBS definition of immigrant status, the country of birth of the person and his/her parents was used to classify ethnic origin. A Dutch-born subject with two Dutch-born parents was considered native Dutch. A Dutch-born subject with at least one foreign-born parent was classified according to the country of birth of that parent. When the parents were born in different foreign countries, the maternal country of birth was decisive for assignment to a particular group. Most ethnic minorities in the study area originated from Turkey, Morocco, Surinam and the Netherlands Antilles. The latter two groups of migrants from former Dutch colonies with relative geographical proximity were collapsed into a single group in the analyses. Other ethnic minorities were categorized in non-Western (from countries with developing economies) and Western (including both
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countries with developed and countries with transition economies) origin. Utrecht City is divided into ten districts. Each district encloses on average about ten neighborhoods (see ‘‘Appendix: Table 5’’). Within each district and within each neighborhood separately (N = 98), the percentage of observation time during 2000–2009 related to a specific ethnic minority group was calculated. For each ethnic group, the selected individual records of the population register were aggregated during these years by district and neighborhood. This was done after weighting by the registered time living in the district and the neighborhood, respectively. The calculated percentages were regarded as measure for own-group minority ethnic density at district and neighborhood level during the study period. These percentages were each highly correlated (r ranged from 0.91 to 0.99) with the proportion of inhabitants with that specific ethnic origin in a certain district and in a certain neighborhood, respectively, on January 1, 2005. The average ethnic density related to all persons from non-Dutch origin was 29.9 % on district level, ranging from districts with 16.4 % to districts with 48.8 %. On a neighborhood level, a similar mean (26.8 %) but a much wider range was found (2.9–82.8 %) (see ‘‘Appendix: Table 5’’). Analysis Cohort study The NAPD rates were analyzed by ethnic density, which was calculated first on district and next on neighborhood level. This was done to find out whether analyzing on a more fine-grained geographical level might lead to different results [6]. Each NAPD case was assigned to the district and neighborhood in Utrecht where he/she was living at the time of first registration of the diagnosis in the PCR-MN. Separate multilevel multivariable Poisson models were designed for the comparison of the NAPD rate among (1) non-Dutch Western persons with the NAPD rate among native Dutch persons and (2) among all non-Western persons with that among native Dutch persons, and so on for (3) Turkish, (4) Moroccan, (5) Surinamese/Antillean, and (6) other non-Western persons. These comparisons were done for different values of the own-group minority density. Thus, for each minority group defined in this manner, district-level and neighborhood-level values for own-group minority density were included in the models. In the analyses with ethnic density on district level, the individual person was the first level and the district was the second level. In the analyses with ethnic density on neighborhood level, the individual person was again the first level and neighborhood was the second level of clustering. As the effect of ethnic origin as first-level characteristic on
psychosis rate may depend on ethnic density of the area of residence as-second level characteristic, the ethnic density hypothesis was tested by inclusion of terms for cross-level interaction of (ethnic origin 9 ethnic density), as was done in earlier studies [3–7]. Ethnic density was included as a measure categorized in tertiles and as continuous measure in two separate models. Age, gender, and ethnic origin were included as individual-level covariates, and minority density was included as district/neighborhood-level covariate. The neighborhood-level analyses were also adjusted for mean income of the neighborhood to find out whether differences in socioeconomic status (SES) might explain the association between ethnic density and NAPD rates. The number of districts (N = 10) was too small to include an additional second-level covariate. A decrease of the rate ratio (RR) of NAPD among those belonging to an ethnic minority compared to native Dutch persons with increasing minority ethnic density was hypothesized. This decrease may be the result of either a decreasing NAPD rate among those of foreign origin or an increasing rate among the native Dutch (or both). The Poisson model makes it possible to disentangle the between-group and within-group effects of minority density underlying such an interaction effect. All analyses were repeated (1) with restriction to the observation time and NAPD cases among those aged 18–30 years and (2) the observation time and cases registered in 2005–2009. These sensitivity analyses were done to explore whether the results were sensitive to restriction to a sample of cases that were more likely to be treatment incident and necessarily have a short illness duration at the time of earliest registration of the NAPD diagnosis in the PCR-MN. The nested case–control study To find out whether differences in rates of moving house prior to registration of NAPD from high- to low- or low- to high-density setting might explain the observed ethnic density effect, a nested case–control study was performed. NAPD cases with an earliest registered diagnosis in 2005–2009 (N = 1,073) were selected. For each case, four control persons without NAPD were randomly selected from the whole population cohort, matched by gender, year of birth, ethnic origin and ethnic density of the neighborhood of residence at the time of NAPD registration of the patient (N = 4,178). It was assessed whether the patient and the matched controls moved house from a setting with a lower to a setting with a higher ethnic minority density (as measured in tertiles) and/or in the reverse direction during the 5 years prior to the patients’ date of earliest NAPD registration (the ‘index date’). Differences in percentages between cases and controls with at least one such
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Soc Psychiatry Psychiatr Epidemiol Table 1 Demographic characteristics of sample and denominator population NAPD N (%)
Unique persons N/person years N (%)
2,064 (100 %)
404,595/2,241,320 (100)
1,180 (57.2 %) 884 (42.8 %)
191,785/1,065,099 (47.5) 212,810/1,176,221 (52.5)
18–30
506 (24.5)
213,230/684,690.5 (30.5)
30–40
539 (26.1)
141,686/536,110.7 (23.9)
40–60
697 (33.8)
113,519/619,226.0 (27.6)
[60
322 (15.6)
66,921/401,293.0 (17.9)
1,242 (60.2 %)
284,747/1,625,469 (72.5)
Total Gender Male Female Age (years)
Ethnicity Dutch
Results Description
Other Western
237 (11.5 %)
52,765/239,064 (10.7)
Turkish
81 (3.9 %)
12,309/80,691 (3.6)
Moroccan
222 (10.8 %)
21,409/144,999 (6.5)
Surinamese/Antillean
155 (7.5 %)
13,404/71,653 (3.2)
Other non-Western
127 (6.2 %)
20,230/79,444 (3.5)
Year of diagnosis 2000–2002 2003–2005
603 (29.2 %) 605 (29.3 %)
2006–2007
469 (22.7 %)
2008–2009
387 (18.8 %)
Subdiagnosis of NAPD Schizophreniaa
928 (45.0 %)
Schizophreniformb/Affectivec/delusional disorderd
346 (16.8 %)
Psychotic disorder othere or NOSf
790 (38.3 %)
NAPD non-affective psychotic disorders a
DSM-IV codes 295.20, 295.10, 295.30, 295.60, 295.90
b
295.40
c
295.70
d
297.1
e
298.80, 297.30, 293.81, 293.82
f
298.90
transition were assessed for all ethnic groups separately and tested in a logistic regression model. It was hypothesized that NAPD cases of Dutch origin more often moved to a neighborhood with a lower SES during the prodromal or early stages of NAPD (‘social drift’). As these neighborhoods are most often also characterized by high ethnic minority density, this might (partly) explain the (possible) trend toward lower RR among ethnic minorities compared to the Dutch in high-density areas. For ethnic minorities, a drift to areas with similar or lower SES, but with lower
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own-group minority density during the prodromal or early stages of NAPD might theoretically explain a density effect as well. However, this seems less obvious, if not impossible. Ordinary logistic regression was used with and without adjustment for the matching factors. Data-management, record linking, the sampling of controls, and logistic regression were performed with SPPS, version 14.0. The multilevel Poisson regression analysis was performed with STATA, version 11.0, using procedure GLAMM [12].
The population of Utrecht City in the period 2000–2009 consisted of 404,595 (whole period) unique persons aged 18 years and older, who contributed with 2,241,320 person years of observation to the present analysis. Among these persons and during these years, 2,064 cases of NAPD were registered in the PCR-MN during 2000–2009. The mean age at earliest registration of diagnosis in the PCR-MN was 43.0 years. In Table 1, the characteristics of these cases and the source population are given. Non-Western and Western minorities compared to native Dutch The adjusted RR of NAPD among non-Western compared to Dutch persons decreased from 2.26 in districts with low nonWestern minority density (\21.2 %) to 1.51 in districts with high non-Western density (C38.4 %). This resulted in statistically significant terms for (ethnic density 9 ethnic origin) interaction (P = 0.016 when using a categorized measure, and P = 0.001 when using a continuous measure for ethnic density) (Table 2). This interaction appeared to be the result of slightly higher NAPD rates among Dutch persons (RR = 1.39, NS) and slightly lower NAPD rates among non-Western persons (RR = 0.93, NS) in districts with high non-Western minority density compared to districts with low density. When analyzing the data on a neighborhood level, similar but more pronounced results were found. Again, the RRs of NAPD among non-Western persons compared to native Dutch persons clearly decreased with increasing ethnic density. Without adjustment for mean income as neighborhood-level covariate, the NAPD rates among the Dutch majority population significantly increased with higher non-Western minority density (RR = 1.31 and 1.49, P \ 0.05). After adjustment for mean income of the neighborhood, this increasing trend became substantially less strong (P = 0.067). The NAPD rates among the non-Western minorities, on the other hand, showed more pronounced
Soc Psychiatry Psychiatr Epidemiol Table 2 Rate ratios (RRs) of NAPD among non-Western minorities compared to the Dutch by district/neighborhood ethnic density (‘between groups’) and among high-density districts/neighborhoods compared to low-density districts/neighborhoods by ethnic group (‘within’) Between groups: RR of NAPD non-Dutch vs. Dutch (=#ref)
Within ‘Dutch’: RR of NAPD high vs. low density
Within ‘non-Dutch’: RR of NAPD high vs. low density
All non-Western minorities Without adjustment for SES Ethnic density–district (N of Dutch/N of non-Dutch cases) \21.2 % (N = 626/167) 2.26 [1.84–2.79] 21.2–38.4 % (N = 335/180) C38.4 % (N = 281/238)
2.02 [1.65–2.47]
1.00 (=#ref)
1.00 (=#ref)
0.97 [0.61–1.57]
0.87 [0.48–1.57]
1.51 [1.24–1.83]
1.39 [0.84–2.32]
0.93 [0.50–1.74]
Ix: P = 0.016 (df = 2, cat.)
P = 0.254 (df = 2, cat.)
P = 0.901 (df = 2, cat.)
Ix: P = 0.001(df = 1, cont.)
P = 0.466 (df = 1, cont.)
P = 0.622(df = 1, cont.)
Ethnic density–neighborhood (N of Dutch/N of non-Dutch cases) \21.8 % (N = 827/222)
2.38 [2.03–2.79]
1.00 (= #ref)
1.00 (=#ref)
21.8–43.3 % (N = 297/197)
1.72 [1.42–2.08]
1.31 [1.01–1.71]
0.95 [0.72–1.24]
C43.3 % (N = 118/166)
1.24 [0.96–1.61]
1.49 [0.99–2.25]
0.78 [0.54–1.12]
Ix: P \ 0.001 (df = 2, cat.)
P = 0.031 (df = 2, cat.)
P = 0.419 (df = 2, cat.)
Ix: P \ 0.001(df = 1,cont.)
P = 0.002 (df = 1, cont.)
P = 0.142 (df = 1, cont.)
With adjustment for SES Ethnic density–neighborhood \21.8 %
2.36 [2.02–2.76]
1.00 (= #ref)
1.00 (= #ref)
21.8–43.3 % C43.3 %
1.71 [1.41–2.07] 1.24 [0.96–1.61]
1.23 [0.93–1.62] 1.35 [0.85–2.14]
0.89 [0.67–1.18] 0.71 [0.47–1.08]
Ix: P \ 0.001 (df = 2, cat.)
P = 0.211 (df = 2, cat.)
P = 0.28 (df = 2, cat.)
Ix: P \ 0.001(df = 1,cont.)
P = 0.067 (df = 1, cont.)
P = 0.074 (df = 1, cont.)
Adjusted for age and gender SES socioeconomic status, measured as mean income of neighborhood and included as second-level covariate, Ix interaction effect of (ethnic density 9 ethnic origin), cat. ethnic density included as categorized variable, in tertiles, as shown, cont. ethnic density included as continuous variable, in %
decrease with higher non-Western minority density, reaching the level of borderline significance (P = 0.074). A similar picture of decreasing RRs of NAPD among Western minorities compared to native Dutch with higher Western minority density was found. However, this finding was fully explained by increasing NAPD rates among the Dutch with increasing Western minority density (Online supplement: Table S.1). When restricting the analyses to the observation time and NAPD cases at ages 18–30 years (506 cases in 684,690.5 person years), a similar decrease of betweengroup RRs with increasing neighborhood ethnic density was found in the analysis for non-Western minorities (P value for interaction = 0.003, continuous) (Online supplement: Table S.2). After adjustment for SES, the within-group differences were also similar in direction and magnitude, but in statistical terms less pronounced (P = 0.112 among the native Dutch, and P = 0.123 among the non-Western persons). For non-Western minorities, the analysis was also restricted to the observation time and NAPD cases in the years 2005–2009. This was done to achieve a higher proportion of incident cases,
as newly registered patients in the first 5 years of a register are likely to contain a high proportion of prevalent rather than incident cases. The effect sizes were similar in magnitude and direction, but the effect estimates for the withinnon-Western group comparison became far from statistically significant (data not shown). Separate non-Western minority groups Among all separate non-Western minorities, decreasing RRs of NAPD compared to native Dutch persons with increasing own-group density were found, resulting in significant terms for (ethnic density 9 ethnic origin) interaction (P values \0.001–0.044, continuous measure) (Table 3). Also, for these minorities in the within-group comparisons, decreasing trends of NAPD rates associated with higher own-group ethnic density were found. For the Surinamese/Antillean persons, this decreasing trend was highly significant (P = 0.001), and for non-Western persons in the category ‘other’, this trend was borderline significant (P = 0.073). When restricting the analyses to those aged 18–30 years, the trend in the between-group RRs of NAPD among the
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Soc Psychiatry Psychiatr Epidemiol Table 3 All non-Western minorities, separately for Turkish, Moroccan, Surinamese/Antillean and other non-Western minorities Between groups: RR of NAPD non-Dutch vs. Dutch (=#ref)
Within ‘Dutch’: RR of NAPD high vs. low density
Within ‘non-Dutch’: RR of NAPD high vs. low density
Turkish Ethnic density–neighborhood (N of Dutch/N of non-Dutch cases) \6.5 (N = 892/26)
1.39 [0.93–2.08]
1.00 (=#ref)
1.00 (=#ref)
6.5–9.6 % (N = 235/29)
1.19 [0.80–1.76]
1.13 [0.81–1.59]
0.97 [0.52–1.78]
C9.6 % (N = 115/26)
0.78 [0.49–1.25]
1.13 [0.71–1.78]
0.63 [0.32–1.26]
Ix: P = 0.044 (df = 1, cont.)
P = 0.336 (df = 1, cont.)
P = 0.288 (df = 1, cont.)
Moroccan Ethnic density–neighborhood (N of Dutch/N of non-Dutch cases) \11.3 % (N = 977/83)
2.18 [1.72–2.77]
1.00 (=#ref)
1.00 (= #ref)
11.3–27.6 % (N = 194/82)
1.79 [1.37–2.34]
1.25 [0.88–1.76]
1.02 [0.68–1.54]
C27.6 % (N = 71/57)
1.01 [0.70–1.47]
1.38 [0.80–2.39]
0.64 [0.37–1.10]
Ix: P \ 0.001 (df = 1, cont.)
P = 0.056 (df = 1, cont.)
P = 0.157 (df = 1, cont.)
Suriname/Antillean Ethnic density–neighborhood (N of Dutch/N of non-Dutch cases) \3.2 % (N = 676/61)
3.44 [2.61–4.53]
1.00 (= #ref)
1.00 (= #ref)
3.2–4.9 % (N = 369/57)
2.32 [1.73–3.12]
1.34 [1.03–1.75]
0.91 [0.58–1.42]
C4.9 % (N = 197/37)
2.12 [1.43–3.14]
0.83 [0.60–1.14]
0.51 [0.30–0.86]
Ix: P = 0.001 (df = 1, cont.)
P = 0.664 (df = 1, cont.)
P = 0.001 (df = 1, cont.)
Other non-Western Ethnic density–neighborhood (N of Dutch/N of non-Dutch cases) \3.5 % (N = 641/46)
2.74 [2.01–3.74]
1.00 (= #ref)
1.00 (= #ref)
3.5–6.3 % (N = 405/44) C6.3 % (N = 196/37)
2.09 [1.51–2.89] 1.35 [0.92–1.98]
1.15 [0.90–1.48] 1.37 [0.97–1.93]
0.88 [0.57–1.35] 0.67 [0.42–1.08]
Ix: P = 0.001(df = 1, cont.)
P = 0.008 (df = 1, cont.)
P = 0.073 (df = 1, cont.)
Adjusted for age, gender, and SES SES socioeconomic status, measured as mean income of neighborhood and included as second-level covariate, Ix interaction effect of (ethnic density 9 ethnic origin), cont. ethnic density included as continuous variable, in %
Turkish (from 2.32 to 0.99) and the Moroccan persons (from 4.02 to 1.79) compared to the native Dutch were more pronounced (Online supplement: Table S.2). Among the Moroccans, the within-group decrease of NAPD rates with higher own-group density was statistically significant (RR of NAPD in neighborhoods with Moroccan density of C27.6 % compared to neighborhoods with Moroccan density \11.3 % = 0.63, P = 0.046, continuous). Among the Surinamese/Antillean persons, the within-group decreasing trend disappeared. Among other non-Western persons, the results were similar to the non-restricted analysis. When restricting the analysis to the observation time and NAPD cases in the years 2005–2009, again the effect estimates were similar in magnitude and direction, but in statistical sense less pronounced (data not shown). Residential history Among Dutch NAPD patients, a significantly higher rate of moving house from a low to a high minority density (defined as % non-Dutch) neighborhood during the
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5 years prior to the index date was found, compared to Dutch controls (OR = 1.51) (Table 4). As similar results were obtained for the adjusted and non-adjusted analysis (the adjusted ORs were slightly more pronounced), the results of the univariable regression are shown. The OR of moving house from a high to a low non-Dutch ethnic density neighborhood was in the opposite direction (OR = 0.89, P = 0.486). Among ethnic minorities, no significant differences in rates of moving house from low to high or high to low own-group minority density were found, which may be caused by the small numbers and lack of power. Regardless of the statistical significance, the pattern of ORs did not fit in the hypothesis of social drift as explanation for the higher NAPD incidence among ethnic minorities in lowdensity neighborhoods. Compared to Moroccan controls, a (non-significantly) higher rate of moving house to lowdensity neighborhoods (14.0 vs. 9.7 %) and a (non-significantly) lower rate of moving house to high-density neighborhoods (6.6 vs. 11.3 %) among Moroccan NAPD patients prior to their diagnosis were found. This direction
of the ORs in itself is in accordance with the social drift hypothesis as explanation. However, for Turkish and other non-Western minorities, this pattern is fully reversed, and for the Surinamese/Antillean minority the OR of moving house to low-density areas is negligibly different from 1.00 (1.08 and a P value not far from 1.00).
P = 0.546 P = 0.828 P = 0.172
Discussion
P = 0.473 P = 0.486
P = 0.246
b a
OR = 0.47 [0.13–1.67] OR = 1.26 [0.66–2.39] OR = 0.89 [0.64–1.22]
14.9 % 7.7 %
P = 0.574
8.7 %
12.7 %
10.3 % P = 0.705 P = 0.005
7.8 % Transition from high to low minority density, %b
OR = 1.36 [0.46–4.01] OR = 1.16 [0.53–2.51] OR = 1.51 [1.13–2.03]
12.8 %
39 435
7.1 % 8.2 % 7.3 % 10.6 % Transition from low to high minority density, %a
110 2564 641 Persons, N
Cases Controls Cases
Controls
Cases
a
Defined as at least one transition between the date of NAPD diagnosis and 5 years prior to this date. See , but now transition in the opposite direction
OR = 0.77 [0.34–1.75] OR = 1.08 [0.51–2.30] OR = 1.51 [0.83–2.76]
13.0 % P = 0.289
10.4 % 14.0 %
9.7 %
11.8 %
10.9 % P = 0.704 P = 0.140
8.9 % 13.0 %
OR = 1.53 [0.69–3.35] OR = 0.87 [0.42–1.77] OR = 0.55 [0.25–1.21]
270 77
14.6 % 12.9 %
85
6.6 % 9.7 %
453 121 154
11.3 %
302
Controls Cases Controls Cases Controls
Controls
Cases
Other non-Western Surinamese/Antillean Moroccan Turkish Western Dutch
Table 4 Odds ratios (ORs) of moving house from a lower to a higher tertile and from a higher to a lower tertile of neighborhood minority density among NAPD cases compared to matched controls, by ethnic group
Soc Psychiatry Psychiatr Epidemiol
This large cohort study found that the RR of registered NAPD among ethnic minorities was lower when they lived in a neighborhood with a higher proportion of people of their own ethnicity. This favorable association was stronger on neighborhood level than on district level, that is, when assessed on a smaller geographical scale. The association was found among all separate ethnic minority groups, but was in part explained by higher NAPD rates among native Dutch persons living in neighborhoods with high ethnic minority density. The higher rates among Dutch appeared to be (in part) related to social drift to these neighborhoods, as Dutch cases significantly more often had moved from low to high minority density neighborhoods prior to their date of registered NAPD diagnosis than personally matched Dutch controls in the same period. Comparison with earlier studies Our study has a unique contribution to earlier reports by clearly disentangling the between- and within-group effects of ethnic minority density. When evaluating NAPD rates within ethnic minority groups, that is, without comparison with the majority Dutch population, the density effect was found as well, albeit less pronounced and less consistently. Among Western minorities, no such effect and among nonWestern minorities a borderline significant effect on NAPD rates were found, which became more apparent and statistically significant for Surinamese/Antillean individuals and for Moroccan individuals aged \30 years. In the study of Cochrane and Bal in England, a small trend toward lower schizophrenia rates with a higher own-group density was found within the largest foreign-born groups (from the Caribbean, India, Pakistan, and Ireland), which was clear and statistically significant among Irish-born males only [13]. In the study of Halpern and Nazroo, using National Community Survey data, fewer neurotic and psychotic symptoms were reported among foreign people living in districts with high own-group concentration, but with substantial differences in size and statistical significance between different ethnic groups [14]. In this study, adjustment for economic hardship reduced the association among whites, but strengthened the association among ethnic minorities. This is in accordance with the observed
123
Soc Psychiatry Psychiatr Epidemiol
influence of adjustment for mean neighborhood income on the estimates in our study. These findings are also consistent with the influence of downward social drift on NAPD rates in native Dutch, because high minority density neighborhoods are mostly socioeconomically more disadvantaged than low minority density neighborhoods. This also implies that the ethnic density effect among ethnic minorities cannot be explained by social drift. In our study, this conclusion is supported by the observed ethnic density effect within minority groups and the absence of increased odds of moving house to a low own-group minority density neighborhood prior to registration of NAPD. In the recent study of Jarrı´n et al. among 568 Ecuadorian migrants in Spain, contrary to expectation, an unfavorable association with high ethnic density on mental health symptom scores was found, even after adjustment for the average educational attainment of the area of residence [15]. In contrast with most other studies among wellestablished minority communities, this study was related to recently settled migrants, which suggests that the effect of ethnic density, if present, is sensitive to the context of migration history. In the multilevel studies of Kirkbride et al. in Southeast London [4, 5], of Boydell et al. in South London [3], and of Veling et al. in The Hague [7], lower RRs of psychotic disorders associated with increasing minority density were found. However, the comparison with the native majority population living in high ethnic density areas vs. the comparison across different values for area ethnic density within ethnic minority groups was not clearly disentangled. The study of Schofield et al. [6] in which general practice data on a detailed neighborhood level in South East London were analyzed, both between- and within-group effects of ethnic density on psychotic disorders among black residents were found, quite similar to our findings. Strengths and limitations The sample of NAPD cases in the present study is highly representative of patients in Utrecht who receive treatment for NAPD, as the registration of patients of psychiatric services in the Utrecht region by the PCR-MN is almost complete and a high proportion ([80 %) could be matched with a record in the population register of the CBS. Earlier analyses of data from the PCR-MN showed a somewhat lower probability for patients with a foreign origin to have a record linkage to the CBS [11]. Immigrants more often have errors in their registered birth date and illegal immigrants have no record in the population registry. A relative underrepresentation of ethnic minorities with NAPD might be expected, resulting in an underestimation of the rate ratios comparing minorities with native Dutch. This probably does not influence the found associations with ethnic
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density within ethnic groups, as an association between ethnic density of the person his/her living area and probability of record linkage seems not obvious. The population registry of the CBS is complete for all legally residing residents in the Netherlands. Thus, the full source population of the NAPD cases of Utrecht City in the study period was included in the analysis. Most important for the present study, the population register made it possible to assess the residential history of NAPD patients and their matched controls. This study has a unique contribution to earlier reports by examining for the first time whether differences in patterns of moving house prior to registration of NAPD might explain the found associations with ethnic minority density. For the potential confounding effect of SES, mean income at the district and neighborhood level was included as proxy. Adjustment for mean income at the area level is probably not sufficient to fully cover the effect of SES. Other measures such as educational attainment and prevalence of unemployment should be included as well. For ethnic minorities, however, the effect of SES probably counterbalances the effect of ethnic density, as poor mental health often predetermines an individual to live in economically disadvantaged areas, which are often also characterized by overrepresentation of ethnic minority groups. Thus, the unfavorable association with minority density among native Dutch persons after adjustment for SES (Table 2) might in part be explained by residual confounding of SES, whereas the favorable association among minorities was probably still underestimated [14]. Our results indicate that bias due to social drift is an unlikely explanation for the ethnic density effect in ethnic minorities. Even when disregarding the absence of statistical significance, the pattern of ORs did not fit in the hypothesis of social drift as explanation for the higher NAPD incidence among ethnic minorities in low-density neighborhoods. However, our analysis does not elucidate the mechanisms underlying the density effect. Data were restricted to those diagnosed in specialist psychiatric treatment. Worse access to care has been hypothesized for ethnic minorities, in particular when they are less acculturated to the host society [16]. This in turn may be associated with high ethnic density if those who are less acculturated cluster together [14]. In the Netherlands, those from ethnic minorities appear to have fairly good access to ambulatory mental health care [17]. However, differences are present with those from Moroccan origin having a lower, and those from Turkish and Antillean origin a higher, utilization of specialist mental health care [18]. Contrary to expectation, an important indicator of acculturation (communication in Dutch) appeared to be associated with lower uptake of mental health services among Moroccan subjects [19]. As differences in uptake may be
Soc Psychiatry Psychiatr Epidemiol
confounded by differences in the occurrence of specific mental disorders, the issue concerning the presence of real differences in care-seeking behavior and its possible influence on the observed associations with ethnic density remains unsettled [8]. If social causation underlies the found association with ethnic density (perceived), discrimination and racism in a wider host society together with the favorable buffering effects of same-ethnic social networks and supporting communities in the direct area of residence appear to be a plausible explanation [20, 21]. Our analysis was restricted to those with a registered and, thus, a clinical diagnosis of NAPD. Our sample should be regarded as a cohort of mixed incident/prevalent nature, ignoring the time at risk between disease onset and diagnosis, and between diagnosis and registration in the PCRMN [22]. This probably explains the relatively old age of NAPD cases, on average 43.0 years, compared with other studies, e.g. 27 years in the study of Veling et al. [7], 35.4 years in the study of Boydell et al. [3], and 39.2 in the study of Schofield et al. [6]. However, density effects among non-Western minorities were also found in a selected sample of those aged \30 years, which was likely to consist of true treatment-incident cases and cases at an early stage of their illness. Our study was limited to NAPD as outcome. In earlier studies, the most consistent associations between ethnic density and mental health were found for psychotic symptoms and NAPD [8]. In few other studies, the association with ethnic density was evaluated for other disorders, such as depression and anxiety, or scores for mental health in general, but with mixed results [8]. An important outcome that might be helpful to evaluate the effect of ethnic density on mental health is risk of suicide (attempts), as suicide (attempts) may reflect a wide range of troubles, vague illness and well-defined psychiatric disorders [23]. Furthermore, our study was limited to ethnic origin as determinant of main interest. The principle of psychosocial benefit of living among persons like yourself may also be investigated for other dimensions such as sexual orientation, religion, and being long-lastingly unemployed [24].
prior to diagnosis appeared to explain (in part) these higher rates. Studies with other mental health outcome measures, but also including other psychosocial and demographic dimensions, are needed to fully evaluate the importance of living among people of their own group for the etiology and prevention of mental disorders. Acknowledgments The authors like to thank Statistics Netherlands (Centraal Bureau voor de Statistiek, CBS) for kindly providing the data necessary for the present analysis. Furthermore, the authors like to thank the participating psychiatric hospitals and services for providing all data for the Psychiatric Case Register. The authors thank Janneke Giele (Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht) for collecting the data, data management, and support in preparation of the analysis files. Structural funding of the Psychiatric Case Registers was provided by the participating psychiatric hospitals and services and by the Ministry of Health, Welfare and Sport (VWS). Representatives of the participating psychiatric hospitals and services co-decided on research priorities. The VWS had no role in the study design, analysis, and interpretation of the data, in the writing of the present report, and in the decision to submit for publication. Conflict of interest On behalf of all the authors, the corresponding author states that there is no conflict of interest.
Appendix See Table 5.
Table 5 Characteristics of districts and neighborhoods in Utrecht City Average
Range (min–max)
Districts (N = 10) Number of inhabitants 01/01/2005
27,525
12,330–40,090
Ethnic density % non-Dutch
29.9
16.4–48.8
Non-Dutch Western (%)
10.1
7.3–14.0
Non-Western (%)
19.8
7.3–40.7
Turkish (%)
4.2
0.4–10.2
Moroccan (%)
8.0
1.4–21.9
Surinamese/Antillean (%)
3.5
1.8–6.6
Other non-Western (%)
4.0
2.4–6.9
12,900 €
11,000–15,700
Mean net income per inhabitant Neighborhoods (N = 98)
Conclusion and relevance Our study contributes to the evidence that the proportion of own ethnic minority group in the direct living environment may have an important influence on the risk of psychotic disorders. When interpreting strong relative risk estimates for the effects of ethnic density, however, it must be kept in mind that these effects may be explained in part by higher rates of NAPD among natives living in areas with high minority density. Social drift to more disadvantaged areas
Number of inhabitants 01/01/2005
2,808
10–10,320
Ethnic density % non-Dutch
26.8
2.9–82.8
Non-Dutch Western (%)
10.2
2.8–39.3
Non-Western (%) Turkish (%)
16.6 3.3
0.1–77.5 0.0–21.2
Moroccan (%)
6.2
0.0–45.8
Surinamese/Antillean (%)
3.1
0.0–21.3
Other non-Western (%)
3.7
0.0–15.2
12,900 €
6,200–20,800
Mean net income per inhabitant
123
Soc Psychiatry Psychiatr Epidemiol
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