The proposed 4PL+C procedure results in parameter estimates that have a lower MSE than all other tested statistical analysis procedures (Table ??). The improvement is especially pronounced for R b and R t and smaller but still statistically significant for x 50 and H. Among established procedures, 3PLFB yields the lowest MSE for x 50 and H. Histograms of estimates show that none of the procedures have any clear bias (Figure and S2 of Supporting Information 1); the reduced MSE is due to a reduction in variance.