Figure 4: Correlation map of the 139 selected peaks representing 42 peptide isotopic clusters. The correlation map shows the relationship between the integrated intensities of the 42 peptide isotopic clusters across all serum profiles based on Pearson correlation. The color scale is shown on the right side of the figure, whereby positive correlation is indicated with an increased intensity for red, while negative correlation is shown with an increase for blue. We observe (i) that the peaks within a peptide isotopic cluster correlate strongly and positively, and (ii) that some discriminant peptides correlate strongly with others (examples, shown in Box X (3277.7, 3261.6, 3222.5, which are peptide clusters 40, 41 and 42) and Box Y (1533. 2 and 1616.8, peptide clusters 21 and 24).