CRS.5a: Cedergreen-Ritz-Streibig dose-reponse model for describing...

Description Usage Arguments Details Value Note Author(s) References See Also Examples

Description

'CRS.5a', 'CRS.5b' and 'CRS.5c' provide the Cedergreen-Ritz-Streibig modified log-logistic model for describing (inverse u-shaped or j-shaped) hormesis.

'UCRS.5a', 'UCRS.5b' and 'UCRS.5c' provide the Cedergreen-Ritz-Streibig modified log-logistic model for describing u-shaped hormesis.

Usage

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  CRS.5a(names = c("b", "c", "d", "e", "f"), ...)

  UCRS.5a(names = c("b", "c", "d", "e", "f"), ...)

Arguments

names

a vector of character strings giving the names of the parameters.

...

additional arguments to be passed from the convenience functions.

Details

The model function for inverse u-shaped hormetic 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 hormetic patterns is

f(x) = c + d - \frac{d-c+f \exp(-1/x^{α})}{1+\exp(b(\log(x)-\log(e)))}

This model also simplifies to the four-parameter log-logistic model in case f=0 (in a slightly different parameterization as compared to the one used in LL.4).

The models denoted a,b,c are obtained by fixing the alpha parameter at 1, 0.5 and 0.25, respectively.

Value

See cedergreen.

Note

This function is for use with the function drm.

Author(s)

Christian Ritz

References

See the reference under cedergreen.

See Also

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).

Examples

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## 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))

drc documentation built on May 29, 2017, 11:31 a.m.

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