Reliability analysis of the PDQ-39 (German version)

Aim of the study was the German translation and a reliability analysis of the PDQ-39, a quality-of-life questionnaire for Parkinson patients originally developed in England. 105 outpatient as well as inpatient participants were recruited for this study. Inclusion criteria were defined as age greater than or equal to 40, Hoehn and Yahr category greater than or equal to 1 in patients with definite Parkinson's disease (UK Brain Bank Criteria). The translation process was done according to the protocol of the Medical Outcome Trust Boston. Reliability analysis included the evaluation of internal consistency (Cronbachs alpha), item-to-scale-correlation, test-retest reliability and floor and ceiling effects. These reliability parameters of the German PDQ-39 version were comparable with those of the English original. A small difference for Cronbachs alpha was found in only one of eight subscales of this questionnaire. Stratified analysis revealed that for this subscale differences exist between outpatients and inpatients. The German version allows to use the PDQ-39 in German-speaking countries and facilitates the study of health-related quality of life in Parkinson patients especially in international clinical trials.