The comparison of power curves of all F -like test statistics. The x-axis is the average power from analyzing 900 simulated data sets using F1 with tabled p-values. The y-axis is the estimated powers using empirical gene-specific null distributions from 1,000 residual permutations. The upper four plots show the results with restricted residual permutation, while the lower four plots show the results from unrestricted residual permutation. The solid line indicates the empirical average CWER of a statistic is at the prespecified level, and the dashed line shows an inflated empirical average CWER."ce," all genes have common error; "gh," only between-gene heteroscedasticity exists; "wgh," only within-gene heteroscedasticity exists; "bgh," both between-gene and within-gene heteroscedasticity exist.