Figure 1

Illustration of the effect of Z-value data reduction on a variance analysis with two classification criteria. The p-values associated with the effect of the condition studied and the intersection are compared before and after Z reduction. After this step, the effect associated with the probeset is null (data not shown). Prior to Z reduction, the probesets are expressed at variable levels. After reduction, the expression level is standardized for all of the probesets and their individual contributions are balanced during the variance analysis. The genesets analyzed are distributed differently and reveal a more pronounced effect of the condition and/or of the interaction between the condition and the probesets. Put differently, both the strength and variability of the individual answer are revealed by this step.