Power Analysis for Two-Level Multisite Randomized Cost-Effectiveness Trials

Cost-effectiveness analysis is a widely used educational evaluation tool. The randomized controlled trials that aim to evaluate the cost-effectiveness of the treatment are commonly referred to as randomized cost-effectiveness trials (RCETs). This study provides methods of power analysis for two-level multisite RCETs. Power computations take account of sample sizes, the effect size, covariates effects, nesting effects for both cost and effectiveness measures, the ratio of the total variance of the cost measure to the total variance of effectiveness measure, and correlations between cost and effectiveness measures at each level. Illustrative examples that show how power is influenced by the sample sizes, nesting effects, covariate effects, and correlations between cost and effectiveness measures are presented. We also demonstrate how the calculations can be applied in the design phase of two-level multisite RCETs using the software PowerUp!-CEA (Version 1.0).