l2 {drc} | R Documentation |
'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.
l2(fixed = c(NA, NA), names = c("b", "e"), useDer = FALSE)
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! |
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).
See logistic
.
This function is for use with the function multdrc
.
Christian Ritz
Related functions are l3
, l4
, l5
and the more general
logistic
.
## 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)