In Figure 1A we consider two diseases both with heritability of liability, = 0.2, plotting probability of disease (i.e. G01) vs genetic liability (i.e. A). To allow an extreme comparison, one of the diseases has prevalence K = 0.5 and the other, K = 0.01. Figure 1B also considers two diseases with prevalences K = 0.5 and 0.01, but in this case both have = 0.8. In Figure 1A and 1B, the position of the rise in probability of disease along the x-axis reflects the disease prevalence and the steepness of the rise reflects the heritability of the disease. In Figure 1A the distribution of genetic liabilities on the underlying scale is exactly the same for these two diseases, but when K = 0.01 higher genetic liabilities are needed before probability of disease rises above virtual zero (virtual because it is not exactly zero, but very close to zero); similarly for the diseases in Figure 1B. Figure 1C and 1D plot the ROC curves for the diseases considered in Figure 1A and 1B, respectively. These graphs demonstrate firstly (not unexpectedly),
