Evaluation of Reliability and Validity of PDQ-39: Questionnaire in Iranian Patients With Parkinson’s Disease

Abstract

Background: Parkinson's disease is a progressive neurological disease. Measuring quality of life in these patients could be a useful tool for evaluation and prioritization of care services. The 39-item Parkinson's Disease questionnaire (PDQ-39) is an acceptable measure to assess quality of life in these patients. This study aims to assess the validity and reliability of the Persian version of PDQ-39 questionnaire. Materials and Methods: In this cross-sectional study, Persian version of questionnaire was prepared with translation, back translation, cognation debriefing and culture adaptation. One hundred four Parkinson's disease patients referred to Shahid Motahari clinic affiliated to Shiraz University of Medical Sciences were included in the study. Then PDQ-39 and general quality of life questionnaire (36-Item Short Form Health Survey: SF-36) were completed by trained interviewers. The reliability of the questionnaire was measured through Cronbach's alpha coefficient. Construct validity assessed by item-scale correlation method and criterion validity was determined by discriminant validity and convergenent validity methods. Results: Range of Cronbach's alpha coefficient for different dimensions varied from 0.64 to 0.92. Cronbach's alpha coefficient was higher than 0.70. Item-convergent validity ranged from 0.38 to 0.83. Similar dimensions of PDQ-39 and SF-36 questionnaire were highly correlated. The quality of life among higher stage patients was lower (p<0.001). Conclusion: Findings showed reliability and validity of Persian version of PDQ-39 is acceptable. It can be used to measure health related quality of life in Persian-speaking Parkinson's disease patients.