Quality of life and Parkinson's disease: translation and validation of the US Parkinson's Disease Questionnaire (PDQ-39).

Parkinson's disease is a common progressive neurodegenerative disorder affecting an estimated 4 million people worldwide. A number of general health status measures exist but few fully capture the subjective evaluation of life quality associated with Parkinson's disease. We report here the results of: (1) translating the British PDQ-39 into a US version, (2) validity and reliability of the new US PDQ-39 questionnaire, and (3) parallel validation analyses following the method published in the development of the British version of the PDQ-39. Data were collected by postal survey on 150 patients recruited from neurology clinics in the Seattle area. A short, generic health status measure (SF-36) was used to test convergent validity, and a three-day test-retest assessed the reliability of the PDQ-39. The US version of the PDQ-39 demonstrated acceptable internal consistency (alpha = 0.51 to 0.96) and proved to be reproducible (0.86 to 0.96). Subscales of the PDQ-39 showed convergence with like scales of the SF-36 and was able to discriminate between levels of symptom severity.