Evaluating the psychometric properties of an e-based version of the 39-item Parkinson's Disease Questionnaire

Background: The 39-item Parkinson's Disease Questionnaire (PDQ-39) is the most thoroughly validated and extensively used self-report measure for the assessment of health-related quality of life in people with Parkinson's (PwP). Given the extent of its use and increasing emphasis on electronic data capture, an e-based version of the PDQ-39, the ePDQ, has recently been developed. The aim of this short report is to present some key reliability and validity data that confirm the psychometric quality of the ePDQ. Findings: Participants were emailed a unique link to an online survey incorporating the ePDQ and demographic questions. A total of 118 PwP fully completed the survey. Floor and ceiling effects were calculated to ensure responses were not biased to extreme values. Consequently, score reliability was assessed by item-total correlations with a range from 0.34 to 0.90. Cronbach's alpha was calculated at between 0.64 and 0.95 for the eight domains of the ePDQ. Construct validity was assessed by comparing domain scores in relation to disease duration and gender, with hypothesised differences being largely confirmed. Construct validity was further assessed following a higher order factor analysis which confirmed the appropriateness of calculating a summary index score. Subsequently, significant, but moderate correlations were calculated between the ePDQ summary index score and disease duration and age at diagnosis. Conclusions: Results indicate that the ePDQ largely mirrors the properties of its parent instrument, the PDQ-39, in terms of reliability and validity. Potential users can therefore incorporate the ePDQ into computer-based data capture systems with confidence.