Bias in the population of quasar lenses (all and quads only), compared to the extended source simulation. First panel: median log α_sps. Second panel: median M_h at log M_* = 11.5. Third panel: median M_DM, 5 at log M_* = 11.5 and log R_e = 1.2. Fourth panel: median lens axis ratio. Fifth panel: median mass-sheet transformation parameter, defined in Appendix C. In each panel, the dashed line indicates the value of the parent population. Error bars indicate the standard deviation of the mean of the lens sample.