Development and validation of the psoriasis scale among the system of quality of life instruments for chronic diseases QLICD-PS (V2.0)

BACKGROUND AND PURPOSE: Psoriasis (PS) is difficult to cure with a high incidence. Therefore, the quality of life (QOL) of people with Psoriasis has caused widespread concern. Universal scales respond poorly to subtle changes caused by specific diseases, which makes it challenging to fully understand the impact of QOL in patients with psoriasis. In view of the deficiencies of the universal scale and the lack of a specific scale suitable for Chinese cultural background, this study aims to develop the psoriasis scale among the system of QOL instruments for chronic diseases QLICD-PS (V2.0). METHODS: The scale QLICD-PS (V2.0) was developed based on the procedural decision-making approach and the experience of establishing scales at home and abroad. 122 patients with psoriasis were participated in measuring QOL 3 times before and after treatments. The reliability was assessed by test–retest reliability (Pearson’s correlation coefficients) and also internal consistency (Cronbach’s alpha coefficients). Qualitative analysis was adopted to evaluate content validity; item-domain correlation analysis, multi-dimensional scaling analysis, and factor analysis were adopted to evaluate the construct validity; the SF-36 scale was used as the criterion to evaluate the criterion-related validity due to lack of gold standard. Paired t tests were performed to evaluate the responsiveness on each domain/facet as well as the total of the scale, with Standardized Response Mean (SRM) being calculated. RESULTS: The QLICD-PS was composed of the general module including 3 domains (28 items) and the psoriasis specific module (13 items). The Cronbach's α of the specific module, the general module and the total scale of the QLICD-PS was 0.78, 0.87 and 0.74 respectively, the split-half reliability of the specific module, the general module and the total scale was 0.81, 0.91 and 0.81, respectively, both indicating high reliability. Correlation and factor analysis confirmed good construct validity and criterion-related validity. After treatments, the score changes in the total scale were statistically significant with SRM being 0.5, showing moderate responsiveness. CONCLUSION: As the first psoriasis-specific QOL scale developed by the modular approach in Chinese, the QLICD-PS showed good reliability, validity and responsiveness, and could be used to measure the QOL of Patients with psoriasis specifically and sufficiently.