Study design: Translation, cross-cultural adaptation and psychometric testing of self-report outcome measurements.
Objectives: The aims of this study were to adapt the Functional Rating Index (FRI) to Brazilian-Portuguese and to test the psychometric properties of this new questionnaire and the Brazilian-Roland Morris Disability Questionnaire (RMDQ).
Summary of background data: Self-report measures are commonly used in clinical practice and in research studies. Most existing questionnaires were developed in English and there is only 1 Brazilian-Portuguese cross-cultural adaptation of a spine outcome measure.
Methods: The FRI was translated and adapted into Brazilian-Portuguese according to the Guidelines for the process of cross-cultural adaptation of self report measures. The Brazilian-Portuguese FRI and RMDQ were tested for internal consistency, reliability, ceiling and floor effects, construct validity, and responsiveness in 140 low back pain (LBP) patients.
Results: A very high level of internal consistency (Cronbach's alpha = 0.92) and reliability [ICC = 0.95 (95% confidence interval, 0.93-0.97)] was shown for both instruments. The FRI and RMDQ were highly correlated (r = 0.80), while both the FRI and RMDQ were moderately correlated with pain at baseline (r = 0.67 and 0.55, respectively). No ceiling or floor effects were detected; however, the responsiveness of both questionnaires was quite small (RMDQ ES = 0.10 [84% confidence interval, 0.04-0.16] and FRI ES = 0.18 [84% confidence interval, 0.11-0.24]).
Conclusion: The results of this study indicate that the Brazilian-Portuguese versions of the FRI and RMDQ are reliable and valid instruments for the measurement of disability in Brazilian-Portuguese-speaking patients with LBP presenting for physiotherapy treatment. Both instruments are suitable for use in clinical practice and research studies.