drc (version 0.8-2)

bcl3: The three-parameter logistic function with Brain-Cousens' modification

Description

'bcl3' provides the four-parameter function, self starter function and names of the parameters.

Usage

bcl3(names = c("b", "d", "e", "f"), useDer = FALSE)

Arguments

names

a vector of character strings giving the names of the parameters. The default is reasonable.

useDer

logical. If TRUE derivatives are supplied, otherwise they are not supplied. Not implemented!

Value

• See braincousens.

Details

The Brain-Cousens model is given by the expression $$f(x) = 0 + \frac{d-0+fx}{1+\exp(b(\log(x)-\log(e)))}$$ which is a four-parameter model. It is a modification of the three-parameter logistic curve to take hormesis into account.

References

van Ewijk, P. H. and Hoekstra, J. A. (1993) Calculation of the EC50 and its Confidence Interval When Subtoxic Stimulus Is Present, ECOTOXICOLOGY AND ENVIRONMENTAL SAFETY, 25, 25--32.

Examples

model1 <- multdrc(hormesis[,c(2,1)], fct=bcl3())
summary(model1)
ED(model1, c(50))  # compare the parameter estimate and 
                   # its estimated standard error 
                   # to the values in the above paper
rm(model1)