Cognitive Interviewing to Develop a New Health-Related Quality of Life Measure for Parkinson's Disease: The Preference-Based Parkinson's Disease Index (PB-PDI)

Preference-based measures (PBM) for health-related quality of life (HRQoL) are essential in assessing the cost-utility of different treatment options. The preference-based Parkinson's disease Index (PB-PDI) is being developed for people with Parkinson's disease (PD). The aim of this study was to refine the PB-PDI through cognitive interviews with people with PD. Cognitive debriefing was conducted to assess patients' interpretation of items, both in English and French. Participants' feedback guided the iterative modification of the PB-PDI and items were accepted for final inclusion if they were endorsed by three consecutive participants. A total of 16 participants provided feedback on the items, refined the response options, and discussed how to clarify questions. They selected a 2-week timeframe for the PB-PDI recall period. At the end of the cognitive interviews, all seven items and their response options were endorsed in both languages. The cognitive interview process allowed us to refine items and ensure that they were clear in terms of instructions and response options from the perspective of people with PD. The next step will be to elicit preference weights to develop a scoring algorithm and assess its measurement properties.