drc (version 0.8-2)

ml4a: The modified logistic function

Description

'ml4a' provides Cedergreen-Ritz-Streibig's modified logistic dose response function.

Usage

ml4a(names = c("b", "c", "d", "e", "f"), useDer = FALSE)

Arguments

names

a vector of character strings giving the names of the parameters. The default is reasonable (see above).

useDer

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

Value

• See mlogistic.

Details

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

References

Cedergreen, N. and Ritz, C. and Streibig, J. C. (2005) Improved empirical models describing hormesis, Submitted.

See Also

Similar functions are ml4b and ml4c.

Examples

## Modified logistic model
model1 <- multdrc(hormesis[,c(2,1)], fct=ml4a())
summary(model1)
ED(model1, c(50))

rm(model1)