Psychometric validation of the Chinese version of the Scratch Intensity and Impact Scale (SIIS) in patients with chronic pruritus.

BACKGROUND

Chronic pruritus poses a substantial burden on patients, leading to physical discomfort, emotional distress, and psychosocial dysfunction. The Scratch Intensity and Impact Scale (SIIS) is a patient-reported outcome (PRO) measure designed to assess both scratching intensity and its effects on health-related quality of life (HRQoL). However, its psychometric properties have not been validated in a Chinese population. This study aimed to culturally adapt and psychometrically validate the SIIS for Chinese patients with chronic pruritus.

METHODS

The original SIIS was translated into Chinese following a standardized forward-backward translation procedure. In a cross-sectional study, 358 adult patients with chronic pruritus were recruited from Northeast China. Construct validity was assessed by randomly splitting the sample for exploratory factor analysis (EFA; n = 179) with oblique rotation and confirmatory factor analysis (CFA; n = 179). Reliability was evaluated through internal consistency (Cronbach's α and McDonald's ω), split-half reliability, and two-week test-retest reliability. Content validity was examined using content validity indices.

RESULTS

The 13-item Chinese version of the SIIS exhibited a stable two-factor structure, explaining 84.378% of the total variance. Sampling adequacy was confirmed (KMO = 0.948), and Bartlett's test indicated suitability for factor analysis (χ2 = 6798.064, p < 0.001). CFA demonstrated acceptable model fit: chi-square degree of freedom (χ 2/df) = 2.094, root mean square error of approximation (RMSEA) = 0.078, standardized root mean square residual (SRMR) = 0.0188. Comparative Fit Index (CFI) = 0.985, Tucker-Lewis Index (TLI) = 0.981, Normed Fit Index (NFI) = 0.972, and Incremental Fit Index (IFI) = 0.985. Content validity was strong, with a scale-level content validity index (S-CVI) of 0.96 and item-level indices (I-CVI) ranging from 0.83 to 1.00. The scale also showed excellent reliability, including high internal consistency (Cronbach's α = 0.971, McDonald's ω = 0.969), split-half reliability (Spearman-Brown coefficient = 0.904), and strong test-retest stability over 2 weeks (r = 0.958).

CONCLUSION

The Chinese version of the SIIS demonstrates strong psychometric properties, confirming its reliability and validity as a PRO instrument for evaluating scratching intensity and HRQoL impact. In this population, it shows promise as a PRO instrument for adult patients with chronic pruritus due to AD or psoriasis in dermatology settings, pending further validation in broader populations.