The Brain-Cousens hormesis models

braincousens provides a very general way of specifying Brain-Cousens' modified log-logistic model for describing hormesis, under various constraints on the parameters.

Usage

braincousens(
  fixed = c(NA, NA, NA, NA, NA),
  names = c("b", "c", "d", "e", "f"),
  method = c("1", "2", "3", "4"),
  ssfct = NULL,
  fctName,
  fctText
)

Arguments

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 ":"). The order of the parameters is: b, c, d, e, f.
method: character string indicating the self starter function to use.
ssfct: a self starter function to be used.
fctName: optional character string used internally by convenience functions.
fctText: optional character string used internally by convenience functions.

Value

A list containing the non-linear function, the self starter function, the parameter names and additional model specific objects.

Details

The Brain-Cousens model is given by the expression $$f(x) = c + \frac{d-c+fx}{1+\exp(b(\log(x)-\log(e)))}$$ which is a five-parameter model.

References

Brain, P. and Cousens, R. (1989) An equation to describe dose responses where there is stimulation of growth at low doses, Weed Research, 29, 93–96.

Author

Christian Ritz