Background and methods: The Parkinson's Disease Questionnaire (PDQ-39) was the first specific instrument for evaluation of the "health-related quality of life" (QoL) in Parkinson's disease patients. The PDQ-39 has been subjected to adaptation to Spanish language and culture (PDQ-39 Spanish version, PDQ-39SV) and this version has been validated in aspects of internal consistency and construct validity. The present study assess the test-retest reliability and the convergent validity of the PDQ-39SV with a generic QoL instrument (SF-36).
Results: Most of the PDQ-39 dimensions showed an adequate consistency-Cronbach's alpha > 0.7 for six dimensions. As a whole, test-retest reliability resulted satisfactory. Two dimensions-activities of daily living and emotional well-being- showed a low grade significant difference (paired Student t-test, p < 0.05) due to improvement in the second survey (at 10 to 14 days from the first one) perhaps related to adjustments of the treatment at the first visit. A strong association (Spearman r, p < 0.001), indicative of convergent validity, was obtained for the PDQ-39 dimensions and the relevant SF-36 scales, as well as for the physical and mental component summary scores of the SF-36.
Conclusions: Taking into account these results and previous studies, it is concluded that the PDQ-39 SV is a reliable measure that has construct validity.