Psychometric Evidence for an Augmented PDAQ for Improved Measurement of Cognition‐Related IADLs in Parkinson's Disease

BACKGROUND: The Penn Parkinson's Daily Activities Questionnaire-27 (PDAQ-27) is a 27-item measure of cognitive instrumental activities of daily living (IADLs) for Parkinson's disease (PD) patients developed by integrating 12 additional items with the original 15-item PDAQ-15 via mixed-methods research with the goal of creating a more balanced and sensitive instrument. OBJECTIVES: To evaluate the psychometric properties of the PDAQ-27 in a PD cohort using both patient and knowledgeable informant (KI) responses. METHODS: A cross-sectional study of 114 PD participants was conducted. Participants and, when available, KIs completed the PDAQ-27. Psychometric properties were evaluated using Rasch Measurement Theory (RMT) and Classical Test Theory (CTT). Consistency between patient- and KI-reported versions was assessed using RMT framework. RESULTS: The PDAQ-27 demonstrated strong reliability (Cronbach's alpha = 0.95; Person Separation Index = 0.93) and good Rasch model fit, with no significant local dependency or differential item functioning. The PDAQ-27 total score correlated moderately with cognitive tests (eg, DRS-2 total: r = 0.37; MoCA: r = 0.30), and health-related quality of life (HRQoL) measures (eg, PDQ-39 cognition domain: r = 0.65), supporting construct validity. Compared with the PDAQ-15, the PDAQ-27 marginally improved coverage of mild cognitive IADL impairments, though low-end discrimination remained limited. Patient and KI scores were highly correlated and largely equivalent, despite differing response patterns reflecting the different perspectives of patients and KIs. CONCLUSION: The PDAQ-27 is a promising measure of cognition-related IADLs in patients with PD, with solid cross-sectional psychometric performance. Further research on its longitudinal properties will be needed to recommend its future use in PD studies.