CRS.5a {drc} | R Documentation |
'CRS.5a', 'CRS.5b' and 'CRS.5c' provide the Cedergreen-Ritz-Streibig modified log-logistic model for describing (inverse u-shaped) hormesis.
'UCRS.5a', 'UCRS.5b' and 'UCRS.5c' provide the Cedergreen-Ritz-Streibig modified log-logistic model for describing u-shaped hormesis.
CRS.5a(names = c("b", "c", "d", "e", "f")) UCRS.5a(names = c("b", "c", "d", "e", "f"))
names |
a vector of character strings giving the names of the parameters. The default is reasonable (see above). |
The model is given by the expression
f(x) = c + frac{d-c+f exp(-1/x^{α})}{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 u-shaped model is given by the expression
f(x) = c + d - frac{d-c+f exp(-1/x^{α})}{1+exp(b(log(x)-log(e)))}
The a,b,c models are obtained by setting alpha equal to 1, 0.5 and 0.25, respectively.
See cedergreen
.
This function is for use with the function drm
.
Christian Ritz
See the reference under cedergreen
.
Similar functions are CRS.4a
and UCRS.4a
, but with the
lower limit fixed at 0 (one parameter less).
## Modified logistic model lettuce.m1 <- drm(lettuce[,c(2,1)], fct=CRS.5a()) summary(lettuce.m1) ED(lettuce.m1, c(50)) lettuce.m2 <- drm(lettuce[,c(2,1)], fct=CRS.5b()) summary(lettuce.m2) ED(lettuce.m2, c(50)) lettuce.m3 <- drm(lettuce[,c(2,1)], fct=CRS.5c()) summary(lettuce.m3) ED(lettuce.m3, c(50))