R: The Brain-Cousens hormesis models

braincousens {drc} | R Documentation

## The Brain-Cousens hormesis models

### Description

'braincousens' provides a very general way of specifying Brain-Cousens' modified log- logistic model for describing hormesis, under various constraints on the parameters.

### Usage

      braincousens(fixed = c(NA, NA, NA, NA, NA),
      names = c("b", "c", "d", "e", "f"),
      method = c("1", "2", "3", "4"), ssfct = NULL,
      fctName, fctText)

### Arguments

`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 (should not contain ":"). The default is reasonable (see under 'Usage'). The order of the parameters is: b, c, d, e, f (see under 'Details').
`method` | character string indicating the self starter function to use.
`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.

### Details

The Brain-Cousens model is given by the expression

f(x) = c + \frac{d-c+fx}{1+\exp(b(\log(x)-\log(e)))}

which is a five-parameter model.

It is a modification of the four-parameter logistic curve to take hormesis into account proposed by Brain and Cousens (1989).

### Value

The value returned is a list containing the non-linear function, the self starter function, the parameter names and additional model specific objects.

### Note

This function is for use with the function `drm`.

The convenience functions of `braincousens` are `BC.4` and `BC.5`. These functions should be used rather than `braincousens` directly.

### Author(s)

Christian Ritz

### References

Brain, P. and Cousens, R. (1989) An equation to describe dose responses where there is stimulation of growth at low doses, Weed Research, 29, 93–96.

[Package drc version 3.0-1 Index]