Influence of the level of spiking on RMA expression values and distributions of correlation. 1st row: f f = 0.05, 2nd row: f f = 0.2, 3rd row: f f = 1. 1st column scatterplot of the signal after RMA versus the signal before spiking, 2nd column distortion of the correlation distribution – changes after spiking. 500 randomly selected targets and spikes. Even small amount of stray signal may significantly influence correlation. For f f = 0.2, the fold change is not so much affected, but the effect on correlation distortion is almost as large as for f f = 1.