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.