BMC Public Health 2007, 7:27 http://www.biomedcentral.com/1471-2458/7/27 Dependent variables Self-reported mental health was defined in the present study as the self-reported psychiatric illness and psychosomatic complaints. Self-reported psychiatric illness was derived from two ques- tions: 1) "Have you any long-standing illness, after-effects of injury, disability, or other ailment? Name and describe in detail each ailment/illness." The coding group at Statistics Sweden assigned diagnoses according to ICD-9 (even after 1997) to everything the respondents had reported when answering this question. For the present study, all respondents with the diagnoses 290–319 were defined as having a self-reported long-standing psychiatric illness. 2) "Do you have anxiety?" (Yes, severe; Yes, slight; No). Those who answered "Yes, severe" and "Yes, slight" were regarded as having anxiety. All persons who reported having any long-standing psy- chiatric illness (1) and/or anxiety (2) were categorized as having a self-reported psychiatric illness. Psychosomatic complaints were derived from the questions: (1) "Have you experienced any of the following during the last two weeks: (a) often feeling tired; (b) feeling tired during the day; (c) feeling tired in the evenings; (d) suffer- ing from repetitive headaches or migraine; and/or (e) sleeping difficulties?" (Yes/No) (2) "Have you (f) experienced aching in the shoulders or neck; (g) back pain, pain in the hips or sciatica; (h) pain or aching in the hands, elbows, legs, or knees?" (Yes, severe; Yes, slight; No). Those who answered "Yes, severe" or "Yes, slight" were considered to experience aching or pain. Persons reporting three or more of the above complaints (a-h) were considered to have psychosomatic complaints. Independent variables Country of birth was categorized into: - "Sweden" (reference group); - "Poland"; - "Other East European countries" – a composite of Hun- gary, Bulgaria, the Czech Republic, Slovakia, and Roma- nia; and - "The former Soviet Union" – a composite of all 15 former republics. With the exception of the German Democratic Republic (GDR), all the countries once making up the Soviet Bloc were included in the study. The GDR was excluded because it has been coded as "Germany" together with the Federal Republic of Germany in the SALLS database for the majority of the years of the present study. This made it impossible to define people born specifically in the GDR for our 1994–2001 study period. The official date of the creation of the Soviet Bloc is May 14, 1955, although Eastern Europe had de facto already come under Soviet control at the end of the Second World War. Consequently, we chose to include immigrants from the countries of the former Soviet Bloc who came to Swe- den after 1944, rather than after its official date of crea- tion. We have also included immigrants who arrived after its dissolution in 1989 because they had lived in the Soviet Bloc before that date. Other independent variables were: age (the lower age limit was set at 25 when, presumably, the majority of young people start working and living on their own), sex, and marital status ("married/cohabiting"/"single" with or without children under 18 years old). The social network index was based on the frequency of contacts with a close friend (from 1–6 days ago to more than 12 months ago) and the neighborly exchange of small services (from sev- eral times a week to never). The answers were ranked from 0 to 5 and the scores for these answers were added up (range: 0–10). Participants with a score of less than 3 were considered to have a "good" social network, others to have a "poor" social network. The social network variable measured as the frequency of contacts does not reflect the 'extensiveness' and 'resourcefulness' of these contacts; nevertheless, it represents the respondent's potential for obtaining support (emotional or material) if in need. Two proxies of SES, occupation and housing tenure, were included as independent variables as well. Occupational status ("higher and middle white-collar"; "lower white- collar", "self-employed", "student", or "blue-collar worker") was regarded as present or, in cases of current retirement/unemployment, previous work. Housing tenure referred to "owning"/"renting" one's home. The employ- ment variable (employed/unemployed) was not included since it did not allow ordinary pensioners, early retire- ment pensioners, disability pensioners, or students to be taken into account. One variable characterizing the lifestyle of respondents was included in the present analysis, i.e. smoking ("Yes/ No"). However, the choice of the lifestyle variable was Page 5 of 12 (page number not for citation purposes)