Sample size determination for EQ-5D-5L value set studies

The EuroQol 5-Dimension (EQ-5D) is a widely used health status instrument for cost-utility analysis of healthcare interventions. Recently, its 5-Level version (EQ-5D-5L) and a protocol for conducting valuation of its health states were developed. We propose four approaches for estimating the sample size for EQ-5D-5L valuation according to the standardized procedures of the protocol. The first approach is for estimating mean health state utility values with a desired precision level using a regression model. The second approach, empirical in nature, determines a sample size based on mean absolute error in predicting health state values using a large-scale reference study. The last two approaches are for assessing the significance of regression coefficients of health state descriptors and to estimate the regression coefficients with a desired precision for predicting health state utility values. Using data from a Singaporean study, we estimated parameters that are useful for sample size determination, including the design effect. Each of the approaches was illustrated with examples and pragmatic recommendations were provided. Capitalizing on the EQ-5D-5L valuation protocol, we proposed four sample size estimation approaches which can help to decide an appropriate sample size for a value set study.