The study is a population-based cross-sectional health survey carried out in 2007 and 2010 in Switzerland.

Data from the Swiss Immigrant Health Survey 2010 (SMHS) and the Swiss Health Survey 2007 (SHS) were obtained from the Swiss Federal Office of Public Health. The SMHS is a cross-sectional, population-based telephonic survey which intends to monitor health trends in a representative sample of immigrants and has been carried out in 2004 and 2010 so far. Due to economic constraints, the SMHS is limited to a selected number of nationalities. The core study population 2010 comprises permanent residents from Portugal, Turkey, Serbia and Kosovo (n = 1800). Participants aged 17 - 74 were chosen by stratified random sampling (gender, country of birth, duration of stay) from the database of the central immigration information system. The computer-aided telephone interviews were carried out in Portuguese, Turkish, Serbian, Albanian, German, and French. Data of Swiss, German and Italian nationals from the SHS 2007 were pooled with the SMHS data. The SHS intends to monitor health trends in a representative sample of all permanent residents in Switzerland. It was first conducted in 1992 and is repeated every five years. The 2007 sample included over 19,000 subjects aged 15 years or older. Subjects were randomly selected within private households and computer-aided telephone interviews were conducted in German, French and Italian. People who did not speak any of these languages or people who had insufficient language skills were excluded from the SHS. Immigrant participants in both surveys include immigrants and their children, i.e. permanent residents with a non-Swiss nationality.

The response rate of those in the initial SHS sample was 66.2%. 13.2% could not be contacted after numerous contact attempts and 20.6% refused to participate in the SHS. In the initial SMHS national samples, the response rates of nationals from Kosovo, Portugal, Serbia, and Turkey were 50.1%, 51.0%, 46.9%, and 50.8% respec- tively. 35.2% of nationals from Kosovo, 36.4% from Portugal, 30.8% from Serbia and 33.0% from Turkey could not be contacted after numerous contact attempts and 14.7%, 12.6%, 22.3% and 16.2% refused to participate in the SMHS.

In the SMHS, contact attempts were less successful and refusals—with the exception of nationals from Serbia —were less likely as compared to the SHS. Several factors may account for these differences. First, subjects in the SMHS were contacted and interviews conducted in their respective native language whereas subjects in the SHS had to have sufficient French, German or Italian language skills in order to participate. Selection bias due to insufficient language skills may have been mitigated in the SMHS, i.e. refusal rates were lower because the selection process is less likely to favour immigrants who are well-integrated, well-educated and have been living in Switzerland for a long period of time. Second, potential SMHS participants may have been more difficult to contact because they were younger on average and younger subjects may tend to spend more time outside their homes (school, work, leisure). However, we have no data to substantiate these hypotheses because nationality and other important sociodemographic characteristics were not recorded for the initial SHS and SMHS samples.

The pooled sample represents 58.2% of the immigrant population as well as nationals from Switzerland. Of the 1.7 million immigrants in Switzerland, 17.0% are Italian, 14.9% are German, 12.0% are Portuguese, 5.4% are French, 3.6% are Spaniards, 6.9% are from Serbia, 4.1% are Turkish and 3.3% are from Kosovo [48] . Immigrants from France and Spain were not included because of their small sample size in the SHS. All interviews of the subjects in the pooled sample were conducted in their respective native language.

For the purpose of this study, the initial pooled sample was further narrowed down to include only subjects 17 - 64 years old because only few immigrants in the SMHS sample were over 64 years old. The total sample size amounts to 14,637. The sample size by nationality and further characteristics of the pooled SMHS and SHS sample is shown in Table 1.

Health status, the first target outcome of this study, was derived from self-reported data. Participants were asked to report their health by answering the question: “In general, how would you rate your health? (very good, good, fair, poor, very poor)”. Subjects who rated their health status as fair, poor or very poor were assigned to the ill health category, subjected who rated their health status as very good or good were assigned to the good health category. ADL impairments, the second target outcome of this study, was also derived from self-reported data. Participants were asked to report ADL impairment within the last 6 months by answering the question: “During the last six months, how much have you been limited by a health problem in your activities of daily living? (not at all limited, somewhat limited, severely limited)”. Subjects who reported to be somewhat or severely limited were then assigned to the category with and the remaining subjects to the category without ADL impairments.

For the primary predictor, the country of origin, the following nationalities were considered: Portugal, Turkey, Serbia, Kosovo, Germany, Italy and Switzerland. Double citizens who acquired the Swiss nationality through naturalization were considered Swiss. Covariates included: age (measured in whole years), gender (male/female), socio-economic status (SES) and dwelling zone. SES comprised three indicators: education (basic, secondary, and university), employment (economically active [no/yes]), and housing situation (rooms per person). Urbanity comprised two categories: rural area and urban area. Urban areas included isolated cities (≥10,000 inhabitants) and urban agglomerations (≥20,000 inhabitants); all other areas were assigned to the category rural area. Furthermore, two psychosocial resources—sense of mastery and social support—were selected as covariates because of their relevance when coping with stressful life events such as diseases and impairment [49] . While the sense of mastery instrument was based on a brief version of the Pearlin coping questionnaire [50] , the social support instrument was based on the SMHS 5-item social support index.

^aFigures refer to percentage or arithmetic mean and standard deviation (SD) within nationality. ^bIn general, how would you rate your health? (very good, good, fair, poor, very poor). ^cDuring the last six months, how much have you been limited by a health problem in your activities of daily living? (not at all limited, somewhat limited, severely limited). ^dClassification according to the Swiss Federal Statistical Office. Urban areas include isolated cities (≥10,000 inhabitants) and urban agglomerations (≥20,000 inhabitants). ^eBased on the brief version of the Pearlin coping questionnaire. ^fNumber of years passed since immigration to Switzerland (non-Swiss nationals only). ^gBased on the SMHS 5-item social support index (higher values indicate more social support).

The original expansion weights of the SMHS and SHS were used for all population estimates. The weights take into account the different sampling strategies which have been used to sample immigrants and Swiss nationals and they allow correct estimates of population parameters for immigrants and Swiss nationals.

We used STATA Version 12.1 for all statistical analyses. Multivariate logistic regression was employed to as- sess the factors associated with ill health and ADL impairments. We reported adjusted odds ratios (OR), 95% confidence intervals (CI) and P-values. OR were adjusted for age, gender, the interaction between age and gen- der, socio-economic status (including educational level, employment, number of rooms/person), nationality, and the interaction between nationality and age and the interaction between nationality and gender. To incorporate information on the appropriate weights and sampling units for correct variance estimation, all statistical analyses were carried out using STATA’s command for complex surveys (svy prefix). Statistical significance was estab- lished at P ≤ 0.05.

Adjusting for all covariates, we found no main effect of nationality for men, i.e. immigrant men and Swiss men were equally likely to report ill health where as Portuguese women were more likely and German women were less likely to report ill health than Swiss women (Table 2). Overall, ill health was associated with older age in all groups (Figure 1). However, nationals from Turkey and nationals from Kosovo were substantially more likely than Swiss to report ill health with increasing age. Furthermore, subjects with secondary education or a university degree were less likely to report ill health than those with basic education. Economically active sub- jects were less likely to report ill health than subjects who were not economically active. Subjects with more so- cial support and those with medium or high sense of mastery were also less likely to report ill health. Finally, neither housing situation nor the specific dwelling zone was significantly associated with ill health.

In order to control for potential acculturation effects, length of time in Switzerland (years) was added as a co- variate to the model previously discussed and the model was re-estimated using immigrant data only. However, length of time in Switzerland had no statistically significant association with ill health (results not shown).

Adjusting for all covariates, we found that Turkish men and Portuguese men were less likely to report ADL im- pairment than Swiss men where as immigrant women from different nationalities and Swiss women showed tistical significance (Table 2). ADL impairments were associated with older age in Swiss men. Swiss women

^aWeighted data of 17 - 64-year-old subjects, Swiss Immigrant Health Survey 2010 & Swiss Health Survey 2007. Ill health (1/0): 1 = self-rated health. very poor, poor or fair; 0 = self-rated health very good or good. Impairment (1/0): 1 = somewhat/severely limited inactivities of daily living during the last 6 weeks; 0 = not at all limited. ^bBased on the brief version of the Pearlin coping questionnaire. ^cBased on the SMHS 5-item social support index (higher values indicate more social support).

similar odds of reporting ADL impairments, i.e. none of the nation-specific odds ratios for women attained sta- were equally likely to report ADL impairments with increasing age. However, nationals from Turkey and natio- nals from Kosovo were substantially more likely than Swiss to report ADL impairments with increasing age (Figure 2). Furthermore, subjects with secondary education or a university degree were less likely to report ADL impairments than those with a basic education. Economically active subjects were less likely to report ADL impairments than subjects who were not economically active. Subjects with more social support and those with medium or high sense of mastery were also less likely to report ADL impairments. Finally, neither housing situation nor the specific dwelling zone was significantly associated with ADL impairments. Again, length of time in Switzerland (years) was added as a covariate to the model previously discussed and the model was re- estimated using immigrant data only. Length of time in Switzerland had no statistically significant association with ADL impairments (results not shown).