Gamma Dose-Response Model — gammadr • drc

A four-parameter dose-response model derived from the cumulative distribution function of the gamma distribution. Only suitable for increasing dose-response data.

Usage

gammadr(
  fixed = c(NA, NA, NA, NA),
  names = c("b", "c", "d", "e"),
  fctName,
  fctText
)

Arguments

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.
fctName: optional character string used internally by convenience functions.
fctText: optional character string used internally by convenience functions.

Value

A list containing the nonlinear function, the self starter function, and the parameter names.

Details

Following Wheeler and Bailer (2009) the model function is:

$$f(x) = c + (d-c) \cdot \mathrm{pgamma}(b \cdot x, e, 1)$$

References

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.

Author

Christian Ritz