Objective: To evaluate reliability and construct validity of the Norwegian versions of the Roland Morris Disability Questionnaire and the modified Oswestry Disability Index.
Design: Translation of two functional status questionnaires and a cross-sectional study of measurement properties.
Methods: The questionnaires were translated and back-translated following the Guillemin criteria. The Norwegian versions were tested for 55 patients with acute low back pain and 50 patients with chronic low back pain. Test-retest with a 2-day interval was performed in a subsample of 28 patients from the chronic sample. Reliability was assessed by repeatability according to Bland and Altman, intraclass coefficient and coefficient of variation. Internal consistency was assessed by Cronbach's alpha. Concurrent construct validity was assessed with correlations between the questionnaires and the SF-36, Disability Rating Index and pain intensity.
Results: Repeatability of the Roland Morris Disability Questionnaire was 4 points, coefficient of variation 15% and intraclass correlation coefficient 0.89, and of the modified Oswestry Disability Index 11, 12% and 0.88, respectively. Internal consistency was 0.94 for both questionnaires. The questionnaires correlated highly with the physical functioning scale of SF-36, moderately with pain, and low with mental scales of the SF-36.
Conclusion: The reliability and construct validity of the Norwegian versions of the Roland Morris Disability Questionnaire and the modified Oswestry Disability Index are acceptable for assessing functional status of Norwegian-speaking patients with low back pain.