Reliability, validity, and responsiveness of the Japanese version of the Patient-Specific Functional Scale in patients with neck pain

The aims of this study were to translate and culturally adapt the Patient-Specific Functional Scale (PSFS) and validate the Japanese version of the PSFS (PSFS-J) in outpatients with neck pain.The PSFS was translated and adapted into Japanese in accordance with the published guidelines. A total of 103 outpatients with neck pain were recruited for this study. Psychometric evaluation included test-retest reliability, convergent validity by comparing the PSFS-J to the Neck Disability Index (NDI), patient's global impression of change (PGIC), and responsiveness (unpaired t test, minimal detectable change).The intraclass correlation coefficient for test-retest reliability was 0.98 (95% confidence interval = 0.95-0.99). The Pearson correlation coefficient with the NDI was -0.35. The Spearman correlation coefficient showed a strong relationship between the change score in the PSFS-J and PGIC (-0.70). The analysis of responsiveness was calculated with the unpaired t test showing a significant difference between the stable and improved patients (P0.01). The minimal detectable change was calculated as 0.64.The Japanese version of the PSFS is a valid, reliable, and responsive instrument to assess Japanese outpatients with neck pain.