Comparison of Rasch and summated rating scales constructed from SF-36 physical functioning items in seven countries: results from the IQOLA Project. International Quality of Life Assessment

Tests of data quality, scaling assumptions, and reliability of the Danish SF-36

We used general population data (n = 4084) to examine data completeness, response consistency, tests of scaling assumptions, and reliability of the Danish SF-36 Health Survey. We compared traditional multitrait scaling analyses to analyses using polychoric correlations and Spearman correlations. The frequency of missing values was low, except for elderly people and people with lower levels of education. Response consistency was high and compared well with results for the U.S. SF-36. For respondents with computable scales in all eight domains, scaling assumptions (item internal consistency, item discriminant validity, equal item-own scale correlations, and equal variances) were satisfactory in the total sample and in all subgroups. The SF-36 could discriminate between levels of health in all subgroups, but there were skewness, kurtosis, and ceiling effects in many subgroups (elderly people and people with chronic diseases excepted). Concerning correlation methods, we found interesting differences indicating advantages of using methods that do not assume a normal distribution of answers as an addition to traditional methods.

Translation and psychometric evaluation of a Chinese version of the SF-36 Health Survey in the United States

Outcome measures are rapidly becoming standard tools in the assessment of clinical effectiveness and in the measurement of health status in populations. In this article we document the development of a self-administered Chinese version of the Medical Outcomes Study 36-Item Short-Form Health Survey (SF-36) and report the results of psychometric testing among 156 adult Chinese Americans in Boston, Massachusetts. Following the standard guidelines, a Chinese version of the SF-36 was developed through forward-backward translation techniques and committee review. We used psychometric methods to test assumptions underlying construction and scoring of scales and to evaluate the reliability and validity of the Chinese SF-36 as a measure of health status. The preliminary results indicated that missing value rates for the 36 items were consistently low. Item-discriminant validity was high (over 90% scaling successes) for six of the eight scales (Physical Functioning, Role-Physical, Bodily Pain, General Health, Role-Emotional, and Mental Health). Cronbach's alpha coefficient was above 0.70 criterion for all scales except Social Functioning. Reliability estimates also appeared to vary by sample characteristics. We discuss the implications of these findings and identify where further work will be required.

The Danish SF-36 Health Survey: translation and preliminary validity studies

This article reports on the Danish translation of SF-36 and discusses the procedures used for translation improvement, translation evaluation, and scale evaluation. We followed the standard procedures of the International Quality of Life Assessment (IQOLA) Project including forward and backward translation, independent assessment of translation quality, assessment of response-choice weighting through visual analogue scale (VAS) investigations, and psychometric testing of the translated questionnaire. We found that backward translation, independent quality assessment, and VAS studies provided useful information for translation improvement. The Danish SF-36 received a favorable translation evaluation by independent rating; however, interrater agreement was low. Preliminary validity studies generally supported the internal consistency and homogeneity of the Danish SF-36, and the questionnaire performed satisfactorily in distinguishing depressive patients from nonpatients. On the basis of this and other studies, we recommend use of the Danish SF-36 in research.

Methods for validating and norming translations of health status questionnaires: the IQOLA Project approach. International Quality of Life Assessment

This article briefly summarizes methods used in the empirical validation of translations of the SF-36 Health Survey. In addition, information about the IQOLA Project norming protocol and 13 general population norming samples analyzed in this supplement is provided.

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

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.