Normalized GAPDH intensities for all samples. GAPDH was arrayed 304 times on every slide. The mean and percentiles results for GAPDH on all slides. Expression values are plotted as the ratio of Ln sample (Cy5) versus Ln reference material (Cy3). FFPE samples are marked ˚, whereas frozen samples are marked ×. Spot outliers are seen for all samples but more pronounced in FFPE samples.