Functional rating index - A new valid and reliable instrument to measure the magnitude of clinical change in spinal conditions

Study Design. A prospective cohort design was used to evaluate the Functional Rating Index in a multicentered setting with 139 participants. The Functional Rating Index is a self-reporting instrument consisting of 10 items, each with 5 possible responses that express graduating degrees of disability. Objectives. The goal of this study was to evaluate the psychometric qualities of the Functional Rating Index. Summary of Background Data. The Functional Rating Index combines the concepts of the Oswestry tow Back Disability Questionnaire and the Neck Disability Index and seeks to improve on clinical utility (time required for administration). Methods. One hundred thirty-nine subjects with spinal complaints participated in four different cohorts to study reliability, validity, responsiveness, and clinical utility. Results. Reliability: Test-retest: Intraclass correlation coefficient was excellent (ICC3,k = 0.99); interitem correlation: Item efficiency was good, ranging between 0.54 and 0.82, with a moderate correlation among all items; Cronbach's alpha was excellent (0.92). Validity: construct: The Functional Rating index correlated with the Disability Rating index (0.76), the Short Form-12 Physical Component Score (0.76), and the Short Form-12 Mental Component Score (0.36). Responsiveness: Overall, the size effect was 1.24, which is commendable. Clinical utility. Time required by the patient and staff averaged 78 seconds per administration, which is noteworthy. Effect of Sociodemographics: Total scores were not affected by education, gender, nor age, suggesting minimal external validity bias. Conclusions. The Functional Rating index appears to be psychometrically sound with regard to reliability, validity, and responsiveness and is clearly superior to other instruments with regard to clinical utility. The Functional Rating Index is a promising useful instrument in the assessment of spinal conditions.