The model function for the logistic model is defined as $$ f(d, \theta) = E_0 + E_{\max}/\left\{1 + \exp\left[ \left(ED_{50} - d \right)/\delta \right] \right\}$$
logistic(dose, e0, eMax, ed50, delta)Dose variable
Left-asymptote parameter, corresponding to a basal effect level (not the placebo effect, though).
Asymptotic maximum change in effect from the basal level.
Dose giving half of the asymptotic maximum effect.
Parameter controlling determining the steepness of the curve.
Response value
The logistic model is intended to capture general monotone, sigmoid dose-response relationships.
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
betaMod, logistic, sigEmax,
linlog, linear, quadratic,
exponential