Evaluating the content validity of generic preference-based measures for use in Parkinson's disease

BACKGROUND: Generic preference-based measures are used to assess the cost-utility of different interventions in Parkinson's disease (PD). However, the difficulty of using them in people with a particular health condition is that these measures may not encapsulate all of the domains that are impacted by the disease. OBJECTIVE: To contribute evidence towards the content validity of generic preference-based measures in people with PD. METHODS: Participants with PD were interviewed on a personalized measure of quality of life, the Patient Generated Index (PGI). The domains identified with the PGI were then categorized using the WHO's International Classification of Functioning, Disability and Health. The extent to which the generic measures (EQ-5D-5L, SF-6D, HUI II, and HUI III) included domains important to persons with PD was qualitatively evaluated. RESULTS: The study included seventy-six participants with PD (mean age 69 years). Dexterity, the top domain nominated by participants, was only included in 1 out of 4 of the generic measures. Fatigue, another commonly reported problem, was not included in 3 out of 4 measures. Sleep, dyskinesia and bowel/bladder problems were not included in any of the measures. CONCLUSION: Content validity is an essential step in the evaluation of whether a questionnaire truly measures the construct it purports to measure, in this case the construct being health related quality of life (HRQL). This study evaluated the content validity of the EQ-5D-5L, SF-6D, HUI II and HUI III in people with PD, and demonstrated that several important PD specific domains are missing from these measures.