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Psychometric testing of the Persian Functional Rating Index (PFRI).To determine the reliability and validity of the PFRI in Persian-speaking subjects with neck pain (NP).The Functional Rating Index is a self-report questionnaire that can be used for patients with back pain or NP. The PFRI has been recently validated in patients with low back pain, whereas it is not validated in patients with NP.One hundred patients with NP, mean age of 42 years, participated in the study; 50 patients agreed to be tested on 2 occasions during a 7-day interval for the reliability phase of the study. A visual analogue scale, the Neck Disability Index, and the Neck Pain and Disability Scale were also completed to assess validity. Fifty healthy subjects completed the PFRI for discriminative validity.Floor and ceiling effects were not observed. Independent t test showed a statistically significant difference in PFRI total scores between patients and healthy subjects supporting the discriminative validity of the PFRI (P < 0.001). PFRI and visual analogue scale demonstrated concurrent criterion validity, with Pearson correlation coefficients of 0.75 for test and 0.70 for retest. Construct validity was supported by a significant Pearson correlation between the PFRI and the Neck Disability Index (r = 0.72, P < 0.0001) and between the PFRI and the Neck Pain and Disability Scale (r = 0.63, P < 0.0001). Factor analysis revealed a 2-factor solution, which jointly accounted for 64.75% of the total variance. Additional factor analysis suggested 8-item PFRI as a unidimensional functional instrument for patients with NP. Internal consistency for the PFRI was high. (Cronbach α coefficients were 0.88 for test, 0.89 for retest, and 0.89 for 8-item PFRI.) Reproducibility assessed by test-retest reliability was excellent (intraclass correlation coefficient [ICC]agreement of 0.96, P < 0.0001).The PFRI is valid and reliable for use in a Persian-speaking population with NP.