The model function for the Emax model is defined as $$ f(d,\theta)=E_0+E_{max}\frac{d}{ED_{50}+d}$$
emax(dose, e0, eMax, ed50)Dose variable
Placebo effect
Asymptotic maximum change from placebo effect
Dose giving half of the asymptotic maximum effect
Response value
The emax model is used to represent monotone, concave dose-response shapes. To distinguish it from the more general sigmoid emax model it is sometimes also called hyperbolic emax model.
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
Pinheiro, J. C., Bretz, F. and Branson, M. (2006). Analysis of dose-response studies - modeling approaches, in N. Ting (ed.). Dose Finding in Drug Development, Springer, New York, pp. 146--171
sigEmax, logistic, betaMod,
linlog, linear, quadratic,
exponential