Simulation of the effect of noise on Xue et al.’s classification. The four spectral line parameters used in the classification are fm, D0.2, c_γ, and b_γ (see Xue et al. 2008, for details). Four magnitudes are illustrated. for each of these, we plot D0.2 versus fm and c_γ versus b_γ. The selection boxes are shown in each panel. The progressive loss of BHB stars (red crosses) from the selection box is clear. Non-BHB stars (black dots) are not scattered into the boxes at the same rate.