Figure 1

Overview of the classes of controls (internal and external) used within a microarray experiment together with a schematic illustrating the addition of external controls at different steps during sample processing. (a) Overview of the classes of controls (internal and external) used within a microarray experiment. Each class reports on variability originating at multiple stages. (b) Schematic protocol showing the addition of external spike-in polyA+ and hybridization controls at different steps during sample processing.