Differential item functioning in the Danish translation of the SF-36

UMMS Affiliation

Department of Quantitative Health Sciences

Publication Date


Document Type



Adolescent; Adult; Aged; Cross-Cultural Comparison; Denmark; *Health Status Indicators; Humans; Middle Aged; Psychometrics; *Quality of Life; Questionnaires; *Translations


Biostatistics | Epidemiology | Health Services Research


Statistical analyses of Differential Item Functioning (DIF) can be used for rigorous translation evaluations. DIF techniques test whether each item functions in the same way, irrespective of the country, language, or culture of the respondents. For a given level of health, the score on any item should be independent of nationality. This requirement can be tested through contingency-table methods, which are efficient for analyzing all types of items. We investigated DIF in the Danish translation of the SF-36 Health Survey, using two general population samples (USA, n = 1,506; Denmark, n = 3,950). DIF was identified for 12 out of 35 items. These results agreed with independent ratings of translation quality, but the statistical techniques were more sensitive. When included in scales, the items exhibiting DIF had only a little impact on conclusions about cross-national differences in health in the general population. However, if used as single items, the DIF items could seriously bias results from cross-national comparisons. Also, the DIF items might have larger impact on cross-national comparison of groups with poorer health status. We conclude that analysis of DIF is useful for evaluating questionnaire translations.

DOI of Published Version



J Clin Epidemiol. 1998 Nov;51(11):1189-202. Link to article on publisher's site

Journal/Book/Conference Title

Journal of clinical epidemiology

PubMed ID


Related Resources

Link to Article in PubMed