Two-parameter log-logistic function

A two-parameter log-logistic function with lower limit fixed at 0 and upper limit fixed (default 1), primarily for use with binomial/quantal dose-response data.

Usage

LL.2(upper = 1, fixed = c(NA, NA), names = c("b", "e"), ...)

l2(upper = 1, fixed = c(NA, NA), names = c("b", "e"), ...)

Arguments

upper: numeric value, the fixed upper limit (default 1).
fixed: numeric vector of length 2, specifying fixed parameters (use NA for non-fixed parameters).
names: character vector of length 2, specifying the names of the parameters (default: b, e).
...: additional arguments to llogistic.

Value

See llogistic.

Details

The two-parameter log-logistic function is given by the expression $$f(x) = \frac{upper}{1+\exp(b(\log(x)-\log(e)))}$$

Author

Christian Ritz

Examples

earthworms.m1 <- drm(number/total~dose, weights=total,
  data = earthworms, fct = LL.2(), type = "binomial")