Correlation matrix between all normal samples from two studies. The gene-expression profiles of each normal tissue sample were compared to all other normal tissue samples from the other dataset by measuring the correlation across all genes. The normal samples from Hsiao et al.  are presented along the y-axis and samples from Ramaswamy et al.  along the x-axis. The correlation matrix displays each pairwise comparison and each entry is color-coded according to the scale bar to the right of matrix. Black rectangles highlight correlation values between the samples from the same tissues in the two different datasets.