gammadr.RdThe gamma dose-response model is a four-parameter model derived from the cumulative distribution function of the gamma distribution.
gammadr(fixed = c(NA, NA, NA, NA), names = c("b", "c", "d", "e"), fctName, fctText)
| fixed | numeric vector specifying which parameters are fixed and at what value they are fixed. NAs are used for parameters that are not fixed. |
|---|---|
| names | a vector of character strings giving the names of the parameters (should not contain ":"). The default is reasonable (see under 'Usage'). |
| fctName | optional character string used internally by convenience functions. |
| fctText | optional character string used internally by convenience functions. |
Following Wheeler and Bailer (2009) the model function is defined as follows:
$$f(x) = c + (d-c) * pgamma(b*x, e, 1)$$
This model is only suitable for increasing dose-response data.
The value returned is a list containing the nonlinear function, the self starter function and the parameter names.
Wheeler, M. W., Bailer, A. J. (2009) Comparing model averaging with other model selection strategies for benchmark dose estimation, Environmental and Ecological Statistics, 16, 37--51.