title: Reliability and validity of the Chinese version of the Psoriasis Disability Index (PDI) in Chinese patients with psoriasis.
abstract: BACKGROUND
  The Psoriasis Disability Index (PDI) is a widely used instrument to measure the impact of psoriasis on patients. There has not been psychometric evaluation of the Chinese version of PDI. The aim of this study was to evaluate its reliability and validity among Chinese patients with psoriasis.
  
  
  METHODS
  A multi-center, cross-sectional study was conducted at 9 hospitals including patients aged 18 years and over. Reliability was determined by internal consistency using Cronbach's alpha. Validity was assessed through convergent validity and known groups validity. Dimensionality of the PDI was examined by exploratory factor analysis in working patients and nonworking patients respectively.
  
  
  RESULTS
  In all, 831 patients were studied. Internal consistency of the PDI was satisfactory. Cronbach's alpha coefficient was 0.91 for the total score and over 0.70 for each subscale of the PDI. Evidence of convergent validity of the PDI was proved by excellent and moderate to good correlations with the Dermatology Life Quality Index (DLQI) and four subscales of the Short Form-36 (SF-36) (role-physical, bodily pain, social functioning, and role-emotional): r = 0.51-0.78. Known groups validity was confirmed that the PDI score discriminated well among patients with different severity of psoriasis. The dimensionality of the PDI was determined by the presence of two-factor structure for working patients and three-factor structure for nonworking patients which accounted for 57.3% and 62.3% of the variance respectively.
  
  
  CONCLUSIONS
  The Chinese version of the PDI is a reliable and valid instrument to assess the impact of psoriasis on patients' lives and could be used in future quality of life assessment of Chinese patients with psoriasis.
authors.affiliation: Department of Medical Statistics and Epidemiology, School of Public Health, Sun Yat-sen University, 74 ZhongShan Er Road, Guangzhou 510080, China.
authors.forename: Zehui
authors.initials: Z
authors.lastname: He
authors.forename: Chuanjian
authors.initials: C
authors.lastname: Lu
authors.forename: Aihua
authors.initials: A
authors.lastname: Ou
authors.forename: Jiqian
authors.initials: J
authors.lastname: Fang
authors.forename: Dongmei
authors.initials: D
authors.lastname: Wang
authors.forename: Jingwen
authors.initials: J
authors.lastname: Deng
authors.forename: Zhongzhao
authors.initials: Z
authors.lastname: Zhang
authors.forename: Jingjie
authors.initials: J
authors.lastname: Yu
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002681:China; D003430:Cross-Sectional Studies; D004185:Disability Evaluation; D004651:Employment / Q000523:psychology / Q000706:statistics & numerical data; D005163:Factor Analysis, Statistical; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011565:Psoriasis / Q000175:diagnosis / Q000523:psychology*; D011594:Psychometrics / Q000295:instrumentation*; D011788:Quality of Life; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D012871:Skin Diseases; D012919:Social Behavior; D011795:Surveys and Questionnaires / Q000592:standards*; D014175:Translating