Reliability and Validity of 39-Item Parkinson's Disease Questionnaire and Parkinson's Disease Quality of Life Questionnaire.

Abstract

Parkinson's disease has a significant impact in quality of life, which can be assessed with 39-item Parkinson's DiseaseQuestionnaire and Parkinson's Disease Quality of Life Questionnaire. This study aimed to evaluate the reliability and validity of thesescales in Portuguese patients. Reliability was assessed through internal consistency (Cronbach's alpha) and reproducibility (intraclasscorrelation coefficient). Regarding construct validity, we performed one-way analysis of variance across different groups according tomodified Hoehn and Yahr scale. For criterion validity, we compared both scales with each other and with the Short Form 36-item HealthSurvey. In a total of 100 patients with Parkinson's disease, Cronbach's alpha ranged for 39-item Parkinson's Disease Questionnairebetween 0.66 - 0.98, and for Parkinson's Disease Quality of Life Questionnaire, between 0.78 - 0.98. Intraclass correlation coefficientfor 39-item Parkinson's Disease Questionnaire ranged between 0.49 - 0.96, and for Parkinson's Disease Quality of Life Questionnaire,ranged between 0.65 - 0.96. Both scales showed, in general, capacity to discriminate differences among patients in the different stagesof disease. The scales presented moderate to strong magnitude correlations with some Short Form 36-item Health Survey domains. Cronbach's alpha coefficients for most domains were satisfactory. Overall, it has been demonstrated good reproducibility,as well as construct and criterion validity. The Portuguese versions of both scales showed to be valid and reliable.