Curve fitting was performed with five methods: our proposed statistical approach and up to four established procedures. Our proposed approach may be summarized as four-parameter fitting to a logistic function with controls (4PL+C). The established procedures are: a fourparameter fit without controls (4PL); a three-parameter fit with fixed bottom such that R b = 0 (3PLFB); a three-parameter fit with a fixed top such that R t = 100 (3PLFT);