Generalised Cedergreen-Ritz-Streibig Model for Hormesis

A six-parameter extension of the Cedergreen-Ritz-Streibig model for describing hormesis, where the alpha parameter is estimated rather than fixed.

Usage

CRS.6(
  fixed = c(NA, NA, NA, NA, NA, NA),
  names = c("b", "c", "d", "e", "f", "g"),
  method = c("1", "2", "3", "4"),
  ssfct = NULL
)

fixed: numeric vector. Specifies which parameters are fixed and at what value they are fixed. NAs for parameters that are not fixed.
names: a vector of character strings giving the names of the parameters (should not contain ":").
method: character string indicating the self starter function to use.
ssfct: a self starter function to be used (optional).

A list containing the nonlinear model function, the self starter function, and the parameter names.

The model function is:

$$f(x) = c + \frac{d-c+f \exp(-1/x^g)}{1+\exp(b(\log(x)-\log(e)))}$$

This generalises the five-parameter CRS.5a model by estimating the alpha exponent (parameter $g$) instead of fixing it.

This function is for use with drm.

Christian Ritz