RESUMO
STUDY DESIGN: A reliability and validity study of a previously translated version of the Roland-Morris Disability Questionnaire (RMDQ). OBJECTIVES: To validate the Turkish version of the RMDQ for use in low back pain. SUMMARY OF BACKGROUND DATA: Clinical and epidemiologic research related to low back pain in the Turkish population would be facilitated by the availability of well-established outcome measures. METHODS: A total of 81 outpatients with low back pain, 64 of whom were followed up on a second occasion, were assessed by the RMDQ. Reliability was assessed using internal consistency and the intraclass correlation coefficient. Internal construct validity was assessed by Rasch analysis; external construct validity was assessed by association with pain and spinal movement. Responsiveness was tested by both the nonparametric and parametric effect sizes. RESULTS: Internal consistency of the RMDQ is found to be adequate (>0.85) at both times, with high intraclass correlation coefficient also at both time points. Internal construct validity of the scale is good, indicating a single underlying construct. Expected associations with pain confirm external construct validity. There is little evidence of differential item functioning. The scale is at the ordinal level. Responsiveness of the RMDQ is good and greater than observed change in spinal movement. CONCLUSIONS: The RMDQ is a robust unidimensional ordinal measure, largely free of differential item functioning, which works well in the Turkish population. Nonparametric effect sizes of ordinal scales are found to overestimate or underestimate the true effect size depending on the nature of the scale and the distribution of patients at baseline.