Cross-cultural adaptation and psychometric properties of the Italian version of the Patient-Specific Functional Scale (PSFS) in subjects with shoulder pain

Abstract

Purpose: To cross-culturally adapt the Patient-Specific Functional Scale (PSFS) into Italian and study its classic psychometric properties in subjects with shoulder pain (SP).

Materials and methods: The PSFS was translated into Italian and administered to 109 SP subjects. Acceptability (time to administer, floor and ceiling effects), reliability (internal consistency [Cronbach's alpha], test-retest reliability [Intraclass Correlation Coefficient (ICC)], and measurement error [Standard Error of Measurement (SEM), Minimal Detectable Change, (MDC)]), were assessed. Moreover, construct validity was investigated through a-priori hypothesis testing, comparing the PSFS with the Disability of the Shoulder, Arm and Hand (DASH) scale, 36-item Short Form Health Survey (SF-36) and Numeric Pain Rating scale (NPRS).

Results: The PSFS was successfully adapted into Italian, and its acceptability was satisfied. Internal consistency was high (Cronbach's alpha = 0.925), and test-retest reliability was good (ICC = 0.866, 95% CI = 0.749-0.931). A SEM of 0.7 points and an MDC of 1.9 points were obtained. We observed moderate evidence for construct validity, with 4/6 correlations between other measures being respected.

Conclusion: This study provided reliability and validity of the PSFS in a sample of Italian SP subjects. Future studies should assess the responsiveness of using the PSFS as an outcome measure to capture clinical changes after treatment.

Keywords: Shoulder pain; patient reported outcome measures; psychometrics; rehabilitation; validation study.