Is health-related quality of life the same for elderly Polish migrants, Turkish migrants and German natives? Testing the reliability and construct validity of the Sf-36 health survey in a cross-cultural comparison

Objective: The Sf-36 is the most widely used instrument to measure health-related quality of life (HRQoL) with the most convincing evidence of both internal consistency and test–retest reliability. In addition, it is appropriate for use among elderly and minority groups like migrants. The aim of this study is to investigate and compare the reliability and the factorial structure of the Sf-36 in a sample of elderly migrants and natives. The hypothesis is that the construct (the HRQoL consisting of eight dimensions correlated with two components) is the same for elderly Turkish migrants, Polish migrants and German natives. This means that the Sf-36 model shows good psychometric properties and model invariance for the three groups investigated in this study. Methods: The Sf-36 v.2 was forward and backward translated to Turkish and Polish. In this cross-sectional study, interviews were conducted with a sample of elderly migrants from Turkey (n = 100), from Poland (n = 103) and a sample of elderly German natives (n = 101). All data were entered and analysed using SPSS version 21 and AMOS Graphics. Cronbach’s α was used to analyse the reliability of the Sf-36. Multi-group confirmatory factor analysis (MGCFA) and structural equation modelling (SEM) were used for the Sf-36 model invariance testing. Results: The reliability of the Sf-36 was good to excellent for all Sf-36 dimensions (α > 0.7) except for General Health (0.55) in the Polish group. Multi-group confirmatory factor analysis (MGCFA) showed non-invariance between the three groups (CMIN: 180.172, df: 51, CMIN/df: 3.533, p < 0.001, CFI: 0.895, RMSEA: 0.092 for the unconstrained model). Model modifications resulted in a good model fit for the Polish group. However, an applicable common Sf-36 model for the three groups was not attained. Conclusion: This study doesn’t support the idea that the factorial structure of the Sf-36 with two components and eight dimensions is the same across three ethnically and culturally diverse groups of elderly subjects. Therefore, comparing subscale scores of the Sf-36 between different ethnic groups may be problematic