multi2.RdThe multistage dose-response model is a combination of log-logistic models that should be useful for describing more complex dose-response patterns.
multi2( fixed = c(NA, NA, NA, NA, NA), names = c("b1", "b2", "b3", "c", "d"), ssfct = NULL, 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'). |
| ssfct | a self starter function to be used. |
| fctName | optional character string used internally by convenience functions. |
| fctText | optional character string used internally by convenience functions. |
The multistage model function with quadratic terms is defined as follows
$$ f(x) = c + (d-c)\exp(-b1-b2x-b3x^2)$$
where x denotes the dose or the logarithm-transformed dose.
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.