Original ArticleTranslation and Performance of the Norwegian SF-36 Health Survey in Patients with Rheumatoid Arthritis. I. Data Quality, Scaling Assumptions, Reliability, and Construct Validity
Introduction
Measurement of health-related quality of life (HRQOL) is often used in clinical trials and in quality control programs in the health care system [1]. From a clinical point of view, it is important to be able to compare results between studies. To do so, the measures must be the same, and they must be reliable and valid. Furthermore, the questionnaire, the scoring methods, and the translation procedures must be standardized.
Measures of HRQOL are usually divided into generic, diagnostic specific, and domain specific (such as fatigue or psychological distress) measures. The generic measures are not specific to any disease or population. Such measures can be used across various diseases while diagnostic specific measures could be used within diagnostic groups and/or studies. Such a modular approach has been adopted by several groups 2, 3.
Several generic measures such as the Nottingham Health Profile (NHP) [4] the EuroQoL Instrument [5], the World Health Organization quality of life (WHOQOL) assessment instrument [6], and the MOS 36-item Short-Form Health Survey (the SF-36) [7] are available. The SF-36 was constructed to produce a brief general measure of health status. It can be used in general population surveys, in clinical research, in daily clinical practice, and other applications in diverse populations [7]. The 36 items in SF-36 are grouped into eight multi-item scales measuring physical functioning, role limitations due to physical problems, bodily pain, general health perceptions, vitality, social functioning, role limitations due to emotional problems, and mental health. An additional item reports health transition over the past year. Item content and response choices are reported elsewhere [7].
To obtain SF-36 translations that could be used in multinational studies, the International Quality of Life Assessment (IQOLA) project was launched [8]. A three-stage program was established including: (1) a rigorous translation and evaluation procedure to ensure conceptual equivalence and respondent acceptance in the various countries; (2) psychometric tests of the hypothesized underlying item scoring and construction of multi-item scales to produce scoring algorithms; and (3) validation and norming studies to evaluate the equivalence of interpretation across countries.
In small countries such as Norway nearly all HRQOL measures must be translated from other languages. Guidelines aiming at achieving translations that allow for comparisons with other countries are therefore of special relevance. The purpose of the present article is to describe the translation of the SF-36 into Norwegian and to present data quality and preliminary tests of the psychometric properties of the SF-36 when administered to a homogeneous patient population with rheumatoid arthritis (RA).
Section snippets
Translation of the Questionnaire
The translation-backtranslation procedure was performed in 1994 following the guidelines of the IQOLA project [9]. The items and response choices were first translated independently by two native speakers of Norwegian. After comparison, discussion with the principal investigator and revision, an agreed upon preliminary version was reached.
Completeness of Data
One or more items were missing in 272 (26%) of the questionnaires. Missing value rates per item ranged from 0.4% (Health Transition) to 9.0% (Role-Emotional number 3), with an average of 4.2% (Table 1). The highest rates of missing data were found in the Role-Emotional scale. The lowest rates of missing values were found in the six items where the response choices followed in a vertical sequence (Bodily Pain numbers 1 and 2, General Health number 1, Social Functioning numbers 1 and 2, and
Discussion
In this study, the Norwegian version of SF-36 was evaluated in patients with rheumatoid arthritis in accordance with standard methodology developed by the IQOLA Project.
The iterative process of translating the SF-36 according to the guidelines set out by the IQOLA Project [9] aims at achieving conceptual and functional equivalence [18]. As reported in previous studies outside the United States 18, 19, some of the moderate physical activities in the Physical Functioning scale are rarely
Conclusion
This study demonstrated that the Norwegian version of SF-36 met scaling assumptions in this population of RA patients. The high rate of missing values in the Role-Emotional scale and suboptimal reliability, item internal consistency and item discriminant validity in the General Health scale called for reassessment of the translation. These revisions were incorporated in Version 1.2 of the form, which was normed in a representative sample of the general Norwegian population. The norm study will
Acknowledgements
The study was financially supported by grant no. 96028/002 from the Norwegian Cancer Society.
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