Q-Q plots. 1A: QQ plot of the intensities of the y(n-2) ions for observed (O) vs. theoretical (T). 1B: QQ plot of the intensities of the y(n-4) ions for observed (O) vs. theoretical (T). In each case, the intensities were normalized to the total intensity of the MAE identified ions in the observed spectra or the total intensity of this subset of ions taken from the theoretical spectra (if total intensity of ions in the theoretical is used, the ratios are distorted by the large number of very weak ions that are not usually observed unless a parent ion is very intense). The vertical lines at the left are those cases where the observed is zero and the theoretical is not. The Q-Q plot shows that the N2 and N4 theoretical distributions deviation similarly from the observed distributions in their lower tails, while the upper N2 tail departs from the expected in a way that N4 does not.