Determination of methods for defining the statistical significance of differentially expressed genes by comparing microarrays and quantitative PCR data. Receiver operating characteristic (ROC) curves associated with using B values (unbroken line) or the absolute fold change (dashed line) to discriminate between genes identified as being differentially expressed or not by QPCR. The area under the curve (AUC) and its standard error (SE) are shown for each variable. The closer the AUC is to 1, the better the variable is at classifying differentially expressed genes.⁴¹