BMC Public Health 2007, 7:27 http://www.biomedcentral.com/1471-2458/7/27 determined by the limitation of our data, namely the incomplete data on other lifestyle characteristics. The following variables were used in the additional anal- ysis as migration-related variables: language spoken at home ("Swedish"/"Other"), and years in Sweden ("1–5", "6–10", "11–19", or "> 20"). Year of immigration to Sweden ("1945–1949"; "1950–1959", "1960–1969", "1970– 1979", "1980–1989", and "1990–1999") is presented in Table 3 as well, but it was not used in the additional anal- ysis (Table 5). This variable highly correlated with years in Sweden and yielded almost the same result, however, with a lower fit of data. Language spoken at home represented mastery of language under the assumption that the general mastery of lan- guage partly depends on whether a person speaks Swedish at home (i.e. constantly, in contrast to immigrants who only use it at work or other public places). Years spent in Sweden and year of immigration to Sweden were included in the study not as proxies of acculturation, but rather to indirectly control for reasons for migration in the defined sample. Statistical methods The data were analyzed using the STATA software package [47]. Unconditional logistic regression [48] was applied to estimate the odds ratios (ORs) of poor self-reported health, and the results were presented with a 95% confi- dence interval (CI). First-order interactions between coun- try of birth and independent variables (excluding migration-related ones) were tested. Full models included these independent variables analyzed jointly. An analysis including the migration-related variables was performed likewise on immigrant groups only (the FSU immigrants were used as a reference). The Hosmer and Lemeshow goodness-of-fit test [49] was used to assess the fit. All models showed a satisfactory fit (p > 0.05). Ethical approval of the study was obtained from the Ethics Committee of the Karolinska Institute, Sweden. Results The three groups of immigrant respondents differed slightly with respect to the descriptive characteristics (Table 3). The largest difference was seen in the year of immigration to Sweden, with immigrants from Poland arriving during 1970–1989, immigrants from the Eastern Europe during 1950–1969 and 1980–1989, whereas immigrants from the FSU mostly arrived right after the war and after 1990 (Table 3). It is noteworthy that the year of immigration to Sweden reflected the occurrence of major events in the countries of birth of these immigrants (Table 1). However, it did not fully mirror the arrival data presented in Table 2. Since the data in Table 2 and the data used for the analysis in the present study stemmed from the same source (Statistics Sweden), this slight discrep- ancy might be explained by the fact that the data in Table 2 were collected during one year (2001), and the data used for the analysis in the present study were pooled from eight years (1994–2001). The personal characteristics (except the migration-related ones) were included in the logistic regression analysis as independent variables. The odds of reporting psychiatric illness and/or psychosomatic complaints varied in differ- ent categories of the independent variables. For example, women reported psychiatric illness and psychosomatic complaints almost twice as often as men. Similarly, respondents occupied with other than the white-color work, respondents who rented their homes, and those who smoked reported psychiatric illness and psychoso- matic complaints more often than their counterparts. Those who were single reported psychiatric illness more often than those who were married/cohabiting, as did respondents with a poor social network, compared to those with a good social network. Most importantly, respondents who were born in Poland or other East Euro- pean countries reported both psychiatric illness and psy- chosomatic complaints almost twice as often as the respondents born in Sweden. When all variables were included in the analysis simultaneously, the odds ratios changed marginally and remained as described above (Table 4). These results suggest that there is an association between the outcomes and several of the independent variables, the association which could not be explained by other included variables. The association between the self- reporting of both psychiatric illness and psychosomatic complaints and the country of birth was the most pro- found: the odds ratios for reporting the outcomes were two times higher among persons born in Poland and other East European countries than among the respond- ents born in Sweden. This association has been tested further. The FSU-born respondents were treated as a reference group, Swedish- born respondents were excluded (Table 5, Models 1a and 1b), and migration-related variables were added one-by- one into the analyses (Table 5, Models 2a, 2b and 3a, 3b). Language at home did not influence the odds of the out- comes, but years in Sweden (Model 3b) largely decreased the odds ratio of reporting psychosomatic complaints among immigrants from Poland and other East European countries. Thus it can be regarded as a confounder for psy- chosomatic complaints, but not for psychiatric illness (Model 3a). 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