The dashed green line shows the ratio of the density function of BHB stars to the density function of all stars. The dot-dashed red line shows the ratio of BHB stars to non-BHB stars from the classification described in Sect. 3.3. This is the same curve plotted in Fig. 3 but it has been renormalized so that the peak is at the same level as the peak of the ratio of density functions – i.e. so that it doesn’t include the simple prior. The dotted blue curve is the result of correcting the basic BHB fraction (dashed green line) for the expected change in the ratio due to noisy spectra. The regions at either end are replaced with a constant value, and the prior actually adopted is plotted as the thick solid black line.