Two-parameter Weibull (type 2) model

A two-parameter Weibull type 2 model with the lower limit fixed at 0 and the upper limit fixed at a specified value. The model is given by the equation $$f(x) = \mathrm{upper} \cdot (1 - \exp(-\exp(b(\log(x) - \log(e)))))$$ This model is primarily intended for binomial/quantal responses.

Usage

W2.2(upper = 1, fixed = c(NA, NA), names = c("b", "e"), ...)

Arguments

upper

numeric value giving the fixed upper limit (default 1).

fixed

numeric vector of length 2, specifying fixed parameters (use NA for parameters that should be estimated).

names

character vector of length 2 giving the names of the parameters (default c("b", "e")).

...

additional arguments passed to weibull2, most notably method (a character string: "1" (default), "2", "3", or "4") which selects the self-starter method for obtaining starting values. See weibull2 for details.

Value

A list of class "Weibull-2" as returned by weibull2.

See also

weibull2, W2.3, W2.4, W1.2

Examples

earthworms.m1 <- drm(number/total ~ dose, weights = total,
  data = earthworms, fct = W2.2(), type = "binomial")