Comparison of the functional rating index and the 18-item Roland-Morris Disability Questionnaire: responsiveness and reliability.

STUDY DESIGN: Retrospective design.

OBJECTIVES: To compare the responsiveness and test-retest reliability of the Functional Rating Index and the 18-item version of the Roland-Morris Disability Questionnaire in detecting change in disability in patients with work-related low back pain.

SUMMARY OF BACKGROUND DATA: Many low back pain-specific disability questionnaires are available, including the Functional Rating Index and the 18-item version of the Roland-Morris Disability Questionnaire. No previous study has compared the responsiveness and reliability of these questionnaires.

METHODS: Files of patients who had been treated for work-related low back pain at a physical therapy clinic were reviewed, and those containing initial and follow-up Functional Rating Index and 18-item Roland-Morris Disability Questionnaires were selected. The responsiveness of both questionnaires was compared using two different methods. First, using the assumption that patients receiving treatment improve over time, various responsiveness coefficients were calculated. Second, using change in work status as an external criterion to identify improved and nonimproved patients, Spearman's rho and receiver operating characteristic curves were calculated. Reliability was estimated from the subset of patients who reported no change in their condition over this period and expressed with the intraclass correlation coefficient and the minimal detectable change.

RESULTS: One hundred and forty-three patient files were retrieved. The responsiveness coefficients for the Functional Rating Index were greater than for the 18-item Roland-Morris Disability Questionnaire. The intraclass correlation coefficient values for both questionnaires calculated from 96 patient files were similar, but the minimal detectable change for the Functional Rating Index was less than for the 18-item Roland-Morris Disability Questionnaire.

CONCLUSION: The Functional Rating Index seems preferable to the 18-item Roland-Morris Disability Questionnaire for use in clinical trials and clinical practice.