Empirical sizes at type I error rate of 0.05 for the case when the genes are weakly correlated (℘ = 0.2). Testing was performed based on (i) sup-statistic with the original kernel (subscript ); (ii) sup-statistic with the kernel PCA including 90% of eigenvalues (subscript ); (iii) score test with ρ fixed at ρ2 (upper bound of ) with original kernel (subscript ); (iv) score test at ρ2 with kernel PCA (subscript ). The null distributions were generated based on (a) the resampling procedure (indexed by P); (b) the χ2 approximation (indexed by χ2 ); and (c) the normal approximation (indexed by N).