Single array ROC curves for fold change and spike-in probes. These ROC curves display the ability to identify differentially expressed probes based on the fold change value. In the spike-in experiment, only the spiked-in probes are present in different quantities in the two channels. The spike-in probes are identified better using median fold changes either with or without background subtraction compared to Agilent processing. Agilent, median with and median without background subtraction, black, red and blue lines respectively.