The model function for the sigmoid Emax model is defined as $$ f(d,\theta)=E_0+E_{max}\frac{d^h}{ED^h_{50}+d^h}$$
sigEmax(dose, e0, eMax, ed50, h)Dose variable
Placebo effect
Asymptotic maximum change from placebo effect
Dose giving half of the asymptotic maximum effect
Hill parameter, determining the steepness of the model at the ED50
Response value
The sigmoid Emax model is an extension of the (hyperbolic) Emax model by introducing an additional parameter h, that determines the steepness of the curve at the ed50 value. The sigmoid Emax model describes monotonic, sigmoid dose-response relationships.
MacDougall, J. (2006). Analysis of dose-response studies - Emax model,in N. Ting (ed.), Dose Finding in Drug Development, Springer, New York, pp. 127--145
emax, logistic, betaMod,
linlog, linear, quadratic,
exponential