RESUMEN
BACKGROUND: Clinicians and researchers commonly use responsive outcome measures to interpret changes in a patient's condition as a result of an intervention. This study was conducted to assess the ability of the Persian version of Neck Disability Index and Functional Rating Index to detect responsiveness in the patients with neck pain. METHODS: A diagnostic accuracy study was done in Ahvaz, Iran, 2016. A convenience sample of 57 Persian-speaking patients with non-specific chronic neck pain completed the Neck Disability Index and the Functional Rating Index at the beginning and after physiotherapy intervention. The responsiveness was investigated by the receiver operating characteristics method and the correlation analysis. Statistical analysis was done using SPSS (version 21), with a P<0.05 as the level of significance. RESULTS: The Functional Rating Index showed that the area under the curve was greater than 0.70 (range=0.651-0.942). The optimal cutoff points for the Functional Rating Index and the Neck Disability Index were 9.5 and 7.5, respectively. Gamma correlation between change scores of the Functional Rating Index and the Neck Disability Index and the Global Rating of Change Scores was 0.53 and 0.33, respectively. CONCLUSION: The results indicated that the Persian version of the Functional Rating Index could detect clinical changes following physiotherapy intervention in a group of patients with chronic non-specific neck pain. Therefore, we recommend that this instrument be used as a responsive measure of neck pain disability in patients with neck pain.