title: Validation of the English version of the Kidney Disease Quality of Life questionnaire (KDQOL-36) in haemodialysis patients in Singapore.
abstract: BACKGROUND
  To validate a widely used health outcomes instrument for patients with chronic kidney disease and on dialysis, the Kidney Disease Quality of Life questionnaire (KDQOL-36), in English-speaking haemodialysis patients in Singapore.
  
  
  METHODS
  This study is a secondary data analysis using the KDQOL-SF (version 1.3) data collected from a cross-sectional survey of haemodialysis patients in Singapore. Cronbach's α was used to test internal consistency reliability. Multi-item scales were assessed using item-to-scale correlation and factor analysis. Both confirmatory and exploratory factor analyses were performed separately for generic and disease-targeted scales. Construct validity was assessed by correlation between disease-targeted and generic scales. Criterion validity was assessed by correlation of the physical component summary (PCS-12) and mental component summary (MCS-12) from KDQOL-36 with the corresponding PCS-36 and MCS-36 from the KDQOL-SF.
  
  
  RESULTS
  Three hundred ninety-four patients who completed the interviews in English [male 55.8 %, mean age (SD) 52.4 (11.7) years] were involved. Kidney disease scales exhibited desirable internal consistency (Cronbach's α 0.822-0.906) and item-to-scale correlation (range 0.763-0.903), and a three-factor model fit the data well [comparative fit index (CFI) 0.934, root mean square error of approximation (RMSEA) 0.085]. For the generic Short Form 12 Health Survey (SF-12) items, a two-factor model (physical and mental) showed poor overall fit, but a three-factor structure (role, physical and mental functions) achieved good model fit (CFI 0.999, RMSEA 0.027). Correlation between disease-targeted and generic scales was weak to moderate (range 0.286-0.418). Correlation between SF-12 and SF-36 was 0.750 for PCS and 0.797 for MCS.
  
  
  CONCLUSIONS
  The English version of the KDQOL-36 appears to be reliable and valid to measure quality of life for haemodialysis patients in Singapore.
authors.affiliation: Saw Swee Hock School of Public Health, National University of Singapore, Singapore, Singapore.
authors.forename: Fan
authors.initials: F
authors.lastname: Yang
authors.forename: Vivian Wei
authors.initials: VW
authors.lastname: Wang
authors.forename: Veena Dhananjay
authors.initials: VD
authors.lastname: Joshi
authors.forename: Titus Wai Leong
authors.initials: TW
authors.lastname: Lau
authors.forename: Nan
authors.initials: N
authors.lastname: Luo
mesh_terms: D003430:Cross-Sectional Studies; D005163:Factor Analysis, Statistical; D005260:Female; D006801:Humans; D007676:Kidney Failure, Chronic / Q000628:therapy*; D008297:Male; D008875:Middle Aged; D011594:Psychometrics; D011788:Quality of Life; D006435:Renal Dialysis; D015203:Reproducibility of Results; D012846:Singapore; D011795:Surveys and Questionnaires; D016896:Treatment Outcome