Description Usage Arguments Details Value Note Author(s) References See Also Examples
'CRS.4a', 'CRS.4b' and 'CRS.4c' provide the Cedergreen-Ritz-Streibig modified log-logistic model for describing hormesis with the lower limit equal to 0.
'UCRS.4a', 'UCRS.4b' and 'UCRS.4c' provide the Cedergreen-Ritz-Streibig modified log-logistic model for describing u-shaped hormesis with the lower limit equal to 0.
1 2 3 |
names |
a vector of character strings giving the names of the parameters. The default is reasonable (see above). |
... |
additional arguments to be passed from the convenience functions. |
The model is given by the expression
f(x) = 0 + \frac{d-0+f \exp(-1/x)}{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) = 0 + d - \frac{d-0+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.5a
and UCRS.5a
,
but with an extra parameter for the lower limit.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 | ## Fitting modified logistic models
lettuce.crsm1 <- drm(lettuce[,c(2,1)], fct=CRS.4a())
summary(lettuce.crsm1)
ED(lettuce.crsm1, c(50))
## Need to explicitly specify that the upper limit
## is the reference in order to get ED10 and ED90 right
ED(lettuce.crsm1, c(10, 50, 90), reference = "upper")
lettuce.crsm2 <- drm(lettuce[,c(2,1)], fct=CRS.4b())
summary(lettuce.crsm2)
ED(lettuce.crsm2, c(50))
lettuce.crsm3 <- drm(lettuce[,c(2,1)], fct=CRS.4c())
summary(lettuce.crsm3)
ED(lettuce.crsm3, c(50))
|
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