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. |
... |
additional arguments to be passed from the convenience functions. |
The model function inverse u-shaped hormesis patterns is
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 log-logistic curve to take hormesis into account.
The parameters have the following interpretations
The model function for u-shaped hormesis patterns is
f(x) = c + d - frac{d-c+f exp(-1/x^{α})}{1+exp(b(log(x)-log(e)))}
The models denoted a,b,c are obtained by fixing the alpha parameter at 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 (the parameter c) fixed at 0 (one parameter less to be estimated).
## 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))