Effect of time on gene expression (Microarray study). A. Time effect within one month: Day 14 vs. Day 28. Each dot corresponds to a probe set. The differences on the vertical axis and the means on the horizontal axis were not computed from the normalized expression values but from the effects (β
time, p) determined by the linear model (see Methods), time being either Day 14 or Day 28; Day 1 was defined as baseline. The model used log2 values for the gene signal intensities. A robust local linear fit of the data is represented as a black line.