Figure 2.

Empirical size/power estimates of the permutation tests (solid lines) and the LRT (dashed lines) for a 0.05 level test of the null hypothesis H₀: no treatment-covariate interaction, for varying magnitude of treatment-covariate interaction effect γ₁₁ and γ₁₂ and error distributions [(a) Lognorm or (b) Pareto], and fixed overall treatment effect α = 0.2 and covariate effects β₁ = 0.2, β₂ = 0.4, based on a total sample size n = 100 (50 subjects in each treatment group)