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

Introduction: Parkinson’s disease has a significant impact in quality of life, which can be assessed with 39-item Parkinson’s Disease Questionnaire and Parkinson’s Disease Quality of Life Questionnaire. This study aimed to evaluate the reliability and validity of these scales in Portuguese patients. Material and Methods: Reliability was assessed through internal consistency (Cronbach’s alpha) and reproducibility (intraclass correlation coefficient). Regarding construct validity, we performed one-way analysis of variance across different groups according to modified Hoehn and Yahr scale. For criterion validity, we compared both scales with each other and with the Short Form 36-item Health Survey. Results: In a total of 100 patients with Parkinson’s disease, Cronbach’s alpha ranged for 39-item Parkinson’s Disease Questionnaire between 0.66 - 0.98, and for Parkinson’s Disease Quality of Life Questionnaire, between 0.78 - 0.98. Intraclass correlation coefficient for 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 stages of disease. The scales presented moderate to strong magnitude correlations with some Short Form 36-item Health Survey domains. Discussion: Cronbach’s alpha coefficients for most domains were satisfactory. Overall, it has been demonstrated good reproducibility, as well as construct and criterion validity. Conclusion: The Portuguese versions of both scales showed to be valid and reliable.