The main finding of this study was that, in general, the HRQL of elderly Iranians in Sweden did not decrease with the time of residence according to dimensions of the SF-36. However, the results of examining whether the length of time since migration to Sweden is associated with HRQL showed few significant differences. Another finding was that the mean scores of HRQL for both Iranian groups were lower than those of the Swedish general population in all dimensions among women and in six of eight dimensions among men. Moreover, the finding indicated that the association between the length of time since migration to Sweden and HRQL varied with sex. Elderly Iranian women with a shorter time of residence in Sweden reported a lower vitality than Iranian women in Iran. Nevertheless, the social functioning and role limitation due to emotional problems increased with additional years in the new country. In contrast, among elderly Iranian men, additional years in Sweden were not associated with HRQL.
Our observation that the elderly Iranian immigrants reported poorer health than Swedes agreed with other studies which have confirmed that foreign-born elderly individuals report poorer health than native-born elderly individuals [9, 10]. The finding that elderly Iranian women with a shorter time of residence in Sweden had an impaired vitality compared to Iranian women in Iran agreed in part with Bentham's theory , which identified poor health as a reason for migration to a new country among elderly people in order to be closer to their families. Meanwhile, the fact that this group of immigrant women is more likely not to experience a poorer HRQL with additional years in Sweden is not in accord with Findley's study , which claims that elderly persons with poor health will be more likely to experience additional impairment of their health after migration.
In this study, the HRQL of elderly Iranians in Sweden was more like that of their countrymen in Iran than that of Swedes. For this reason, we argue that the observed lower HRQL among elderly Iranian immigrants, compared to elderly Swedes, reflects the underlying status of HRQL among people from the country of origin. On the other hand, the finding that length of time since migration to Sweden has no negative effect on health may possibly be due to a quite new migration pattern observed in elderly immigrants in Sweden, which is characterized by travelling between Sweden and their country of origin, spending long periods of time in each country. This new migration pattern has enabled elderly Iranians to succeed in taking advantage of the best of their original culture and the host country's culture .
The higher HRQL among elderly Swedes in this study may be due to potential cross-cultural differences in the perception of health, i.e. differences in perceived health or disease prevalence. In a population-based cross-sectional study from the 2001 California Health Interview Survey, it was estimated that differences in self-reported overall health between different ethnic groups may be due to different perceptions of health that are rooted in culture and language . Moreover, individuals living in different cultural environments with the same disease may perceive their disease differently, which might affect the quality of life in a different way . However, the extent to which cultural differences between elderly Iranians and Swedes influence the reported HRQL is not clear.
The finding of low vitality among Iranian women with a shorter period of residence in Sweden is alarming and might reflect the multiple health problems and high prevalence of CVD risk factors among Iranian women in Iran, which has been documented in many studies [19–25]. However, according to Bentham's theory , poor vitality due to a high prevalence of chronic diseases, such as CVD, might have been a reason for these women to migrate to Sweden.
Socioeconomic status can be measured in different ways, although it is not possible to measure its full dimensions. In the current study, education was used only as a crude proxy of socioeconomic status. At first, we considered using income to characterize socioeconomic status. However, since 76% of the participants arrived in Sweden when they were 50 years of age or older they were not eligible for a full pension and therefore have very low incomes. Because of their limited pension rights and dependency on welfare aid, income is a blunt tool to differentiate individuals by socioeconomic status.
Even using occupation as an indicator of socioeconomic status seems to be less valid in this group of immigrants because nearly all of them are at the age of retirement. In addition, many immigrants in Sweden work in low-status jobs even though they have university degrees. Therefore, education was considered to be a more stable indicator of socioeconomic status in this particular group. Furthermore, education as a measure of socioeconomic status remains fairly unaffected over the course of life and the health status. In addition, health status may influence income and occupation, but not educational status.
One might argue, however, that a sample from Tehran is not necessarily representative of the entire country. In general, this is true, but since Tehran has became a multicultural metropolitan area it has been suggested that a sample from the general population in Tehran could at least be regarded as a representative sample of an urban population in Iran . Regarding the Iranian sample in Stockholm, we studied a population-based representative sample of elderly Iranians in Kista/Stockholm and expect that the result would be generalizable to similar groups residing in other counties in Sweden. However, this expectation remains to be tested.
Limitations and strengths
Some important limitations must be considered when interpreting the results of this study. First, given the cross-sectional nature of the results, the interpretation of the impact of migration on the HRQL is restricted. Future research with a longitudinal approach would be valuable in the area of migrant studies, but very difficult to perform.
The second limitation arises from the fact that we did not control for potentially confounding factors based on objective health status measures, e.g. weight, height, waist measurements, blood pressure, smoking, etc., in our analysis. These measurements are important to consider because of the accumulative prevalence of CVD risk factors in migrant and Iranian populations, particularly in Iranian women. However, objective health status measurements were not available in the data.
Finally, there is a lack of important variables such as social, ethnic, and cultural contexts in either the Stockholm sample or the Iranian sample. Although no previous study has documented an association between ethnicity, culture, and quality of life in Iranian people, we believe that the lack of an analysis of these variables in the results is an important limitation.
Despite the limitations, the present study has some strengths. Although the number of elderly Iranians in Sweden in the study is small, we had sufficient (80%) statistical power to detect medium-sized effects. Moreover, the well-defined control group, which constitutes a random sample of the Swedish population, is also a strength.
Although investigating differences in the HRQL of the two sexes was not one of the aims of this study, it is an important topic that future research can focus on. However, strategies and policies should include a special focus on recently arrived elderly female immigrants who showed a lower HRQL in some of the dimensions, compared to the other elderly Iranian immigrant women and to elderly Iranian women in Iran.