BC.5 {drc} | R Documentation |
'BC.4' and 'BC.5' provide the Brain-Cousens modified log-logistic models for describing u-shaped hormesis.
BC.5(names = c("b", "c", "d", "e", "f")) BC.4(names = c("b", "d", "e", "f"))
names |
a vector of character strings giving the names of the parameters. The default is reasonable. |
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 log-logistic curve to take u-shaped hormesis into account.
Fixing the lower limit at 0 yields the four-parameter model
f(x) = 0 + frac{d-0+fx}{1+exp(b(log(x)-log(e)))}
See braincousens
.
This function is for use with the function drm
or 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.
van Ewijk, P. H. and Hoekstra, J. A. (1993) Calculation of the EC50 and its Confidence Interval When Subtoxic Stimulus Is Present, ECOTOXICOLOGY AND ENVIRONMENTAL SAFETY, 25, 25–32.
lettuce.m1 <- drm(lettuce[,c(2,1)], fct=BC.5()) anova(lettuce.m1) plot(lettuce.m1) lettuce.m2 <- drm(lettuce[,c(2,1)], fct=BC.4()) summary(lettuce.m2) ED(lettuce.m2, c(50)) # compare the parameter estimate and # its estimated standard error # to the values in the paper by # van Ewijk and Hoekstra