W2.Rd'W1.2' is the two-parameter Weibull function where the lower limit is fixed at 0 and the upper limit is fixed at 1, mostly suitable for binomial/quantal responses.
W1.2(upper = 1, fixed = c(NA, NA), names = c("b", "e"), ...) W2.2(upper = 1, fixed = c(NA, NA), names = c("b", "e"), ...)
| upper | numeric value. The fixed, upper limit in the model. Default is 1. |
|---|---|
| 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. |
| ... | additional arguments to be passed from the convenience functions. |
The two-parameter Weibull type 1 model is given by the expression $$ f(x) = \exp(-\exp(b(\log(x)-\log(e)))).$$
The function is asymmetric about the inflection point, that is the parameter \(\exp(e)\).
See weibull1.
This function is for use with the function drm.
## Fitting a two-parameter Weibull model earthworms.m1 <- drm(number/total~dose, weights = total, data = earthworms, fct = W1.2(), type = "binomial") summary(earthworms.m1)#> #> Model fitted: Weibull (type 1) with lower limit at 0 and upper limit at 1 (2 parms) #> #> Parameter estimates: #> #> Estimate Std. Error t-value p-value #> b:(Intercept) 0.475853 0.085228 5.5833 2.36e-08 *** #> e:(Intercept) 0.179730 0.055978 3.2107 0.001324 ** #> --- #> Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1