Measurement of costs and scales for outcome evaluation in health economic studies of Parkinson's disease.

Health economic studies in Parkinson's disease (PD) have become increasingly common in recent years. Because several methodologies and instruments have been used to assess cost and outcomes in PD, the Movement Disorder Society (MDS) commissioned a Task Force to assess their properties and make recommendations regarding their use. A systematic literature review was conducted to explore the use of those instruments in PD and to determine which should be selected for this review. We assessed approaches to evaluate cost of illness (COI), cost effectiveness, and cost utilities, which include the use of direct (standard gamble, time trade-off. and visual analogue scales) and indirect instruments to measure health status and utilities. No validated instruments/models were identified for the evaluation of COI or cost-effectiveness in patients with PD; therefore, no instruments in this group are recommended. Among utility instruments, only a few of these outcome instruments have been used in the PD population, and only limited psychometric data are available for these instruments with respect to PD. Because psychometric data for further utility instruments in conditions other than PD already exist, the standard gamble and time trade-off methods and the EQ-5D (a European quality-of-life health states instrument) and Health Utility Index instruments met the criteria for scales that are "recommended (with limitations)," but only the EQ-5D has been assessed in detail in PD patients. The MDS Task Force recommends further study of these instruments in the PD population to establish core psychometric properties. For the assessment of COI, the Task Force considers the development of a COI instrument specifically for PD, like that available for Alzheimer's disease.