Intrinsically Nonlinear Regression Models - Drug Responsiveness and Half-Maximal Response

In pharmacology, the following model is often used to describe the effects of different dose levels of a drug:

y = b0 - b0/{1 + (x/b2)b1}

In this model, x is the dose level (usually in some coded form, so that x ³ 1) and y is the responsiveness, in terms of the percent of maximum possible responsiveness. The parameter b0 then denotes the expected response at the level of dose saturation and b2 is the concentration that produces a half-maximal response; the parameter b1 determines the slope of the function.