Translation and validation of the Persian version of the 39 item Parkinson’s Disease Questionnaire (PDQ-39)

Background: Health related quality of life is considered to be an important outcome measure in studies involving patients with chronic neurological conditions such as Parkinson’s disease. Disease specific patient reported outcome measures(PROMs) are increasingly used as primary end points in clinical trials of new treatments for such conditions. The most widely used disease specific PROM in PD is the 39 item Parkinson's Disease Questionnaire (PDQ-39). The aim of this study was to determine validity and reliability of Persian PDQ-39. Methods: Two hundred and forty Parkinson’s disease patients attending neurologic clinics of teaching hospitals were recruited. PD patients completed a translated version of the PDQ-39 after giving informed consent. Internal consistency reliability of the questionnaire was assessed by Cronbach's alpha coefficient. Reproducibility (test/retest reliability) was assessed across the 3-week interval using the intraclass correlation coefficient (ICC). To assess convergent validity, results on the PDQ-39 were correlated with those gained on the SF-36, a widely used generic outcome measure. Discriminate validity of