Hierarchical analysis approach. Genes were first classified as EGF responsive by performing a likelihood ratio test to compare the fits of maximum likelihood estimated mixed models with and without EGF terms. EGF responsive genes were then classified as to whether or not they had a significant EGF:CT interaction, as determined by a Wald F-test of the REML estimated full model. EGF responsive genes with EGF:CT interactions were then classified according to whether they were responsive to EGF during the day only, during the night only, or at both times. Genes with significant EGF:CT interactions were then subdivided according to the directionality ofthe responses.
Zak et al. Genome Biology 2006 7:R48 doi:10.1186/gb-2006-7-6-r48