title: Validation of PDQ-8 as an independent instrument in English and Chinese.
abstract: Previous validation studies on the PDQ-8, a brief disease-specific quality of life instrument, were performed with the PDQ-8 nested in the original PDQ-39. Such an approach may influence patient responses and the psychometric properties of the PDQ-8. We therefore undertook this study to validate the PDQ-8 when administered independently in English and Chinese and found good item-to-scale correlations (correlation coefficient: 0.44-0.68) and internal consistency (Cronbach's alpha: 0.81, 0.87). Factor analyses yielded a component on which all 8 questions were substantially loaded (loading range: 0.55-0.77). Scree plots also showed the one-factor solution thereby validating the PDQ-8 summary index. Construct validation against the Hoehn and Yahr stage and UPDRS motor scores showed significant correlations between higher PDQ-8 summary index and increased disease severity in both English and Chinese versions. Our results show the PDQ-8 to be a valid and reliable disease-specific HRQoL instrument for PD when used independently of the PDQ-39.
authors.affiliation: Department of Neurology and Parkinson's Disease and Movement Disorders Centre, National Neuroscience Institute, USA National Parkinson Foundation Centre of Excellence, 11 Jalan Tan Tock Seng, Singapore 308433, Singapore. louis_tan@nni.com.sg
authors.forename: Louis C S
authors.initials: LC
authors.lastname: Tan
authors.forename: Puay-Ngoh
authors.initials: PN
authors.lastname: Lau
authors.forename: Wing-Lok
authors.initials: WL
authors.lastname: Au
authors.forename: Nan
authors.initials: N
authors.lastname: Luo
mesh_terms: D000368:Aged; D044466:Asian People; D018450:Disease Progression; D005260:Female; D006801:Humans; D007802:Language; D008297:Male; D008875:Middle Aged; D009483:Neuropsychological Tests / Q000592:standards*; D010300:Parkinson Disease / Q000523:psychology*; D011237:Predictive Value of Tests; D011788:Quality of Life / Q000523:psychology*; D015203:Reproducibility of Results; D012846:Singapore; D011795:Surveys and Questionnaires / Q000592:standards*