braincousens {drc} | R Documentation |
'braincousens' provides a very general way of specifying Brain-Cousens' modified logistic dose response functions, under various constraints on the parameters.
braincousens(lowerc = c(-Inf, -Inf, -Inf, -Inf, -Inf), upperc = c(Inf, Inf, Inf, Inf, Inf), fixed = c(NA, NA, NA, NA, NA), names = c("b", "c", "d", "e", "f"), scaleDose = TRUE, useDer = FALSE)
lowerc |
numeric vector. The lower bound on parameters. Default is minus infinity. |
upperc |
numeric vector. The upper bound on parameters. Default is plus infinity. |
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'). |
scaleDose |
logical. If TRUE dose values are scaled around 1 during estimation; this is required for datasets where all dose values are small. |
useDer |
logical. If TRUE derivatives are supplied, otherwise they are not supplied. Not yet implemented! |
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.
The value returned by the 'braincousens' is a list with the following components
fct |
The dose response function. |
ssfct |
The self starter function. |
deriv1 |
The first derivative. |
deriv2 |
The second derivative. |
lowerc |
The lower bounds on the parameters. |
upperc |
The upper bounds on the parameters. |
edfct |
The ED function. |
sifct |
The SI function. |
maxfct |
The function for calculating the mean maximum of the dose response curve. |
This function is for use with the function multdrc
.
Christian Ritz
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.
Special cases of the function 'braincousens' are bcl3
and bcl4
.
## Brain-Cousens model with the constraint b>1 model1 <- multdrc(FA, fct=braincousens(fixed=c(NA, NA, NA, NA, NA), lowerc=c(1, -Inf, -Inf, -Inf, -Inf)), control=mdControl(constr=TRUE)) summary(model1) ## Brain-Cousens model with the constraint f>0 model2 <- multdrc(FA, fct=braincousens(fixed=c(NA, NA, NA, NA, NA), lowerc=c(-Inf, -Inf, -Inf, -Inf, 0)), control=mdControl(constr=TRUE)) summary(model2) rm(model1, model2)