l2 {drc}R Documentation

The two-parameter logistic function

Description

'l2' provides the two-parameter logistic function where the lower limit is fixed at 0 and the upper limit is fixed at 1, mostly suitable for binomial/quantal responses.

Usage

  l2(fixed = c(NA, NA), names = c("b", "e"), useDer = FALSE)

Arguments

fixed numeric vector. Specifies which parameters are fixed and at what value they are fixed. NAs for parameter that are not fixed.
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!

Details

The two-parameter logistic function is given by the expression

f(x) = frac{1}{1+exp(b(log(x)-log(e)))}

The function is symmetric about the inflection point (e).

Value

See logistic.

Note

This function is for use with the function multdrc.

Author(s)

Christian Ritz

See Also

Related functions are l3, l4, l5 and the more general logistic.

Examples


## Fitting a two-parameter logistic model 
##  to binomial responses (a logit model)
model1 <- multdrc(number/total~dose, weights=total, 
data=earthworms, fct = l2(), type = "binomial")
plot(model1)  # not fitting at the upper limit!

rm(model1)


[Package drc version 0.9-0 Index]