DIFFERENTIAL ITEM FUNCTIONING IN THE DANISH TRANSLATION OF THE SF-36

Statistical analyses of Differential Item Functioning (DIF) can be use d for rigorous translation evaluations. DIF techniques test whether ea ch item functions in the same way, irrespective of the' country, langu age, or culture of the respondents. For a given level of health, the s core on any item should be independent of nationality. This requiremen t can be tested through contingency-table methods, which are efficient for analyzing all types of items. We investigated DIF in the Danish t ranslation of the SF-36 Health Survey, using two general population sa mples (USA, n = 1,506; Denmark, n = 3,950). DIF was identified for 12 out of 35 items. These results agreed with independent ratings of tran slation quality, but the statistical techniques were more sensitive. W hen included in scales, the items exhibiting DIF had only a little imp act on conclusions about cross-national differences in health in the g eneral population. However, if used as single items, the DIF items cou ld seriously bias results from cross-national comparisons. Also, the D IF items might have larger impact on cross-national comparison of grou ps with poorer health status. We conclude that analysis of DIF is usef ul for evaluating questionnaire translations. (C) 1998 Elsevier Scienc e Inc.