Model diagnostics for nonlinear dose-response models

Description

Hat values (leverage values) and Cook's distance are provided for nonlinear dose-response model fits using the same formulas as in linear regression but based on the corresponding but approximate quantities available for nonlinear models.

Usage

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  ## S3 method for class 'drc'
cooks.distance(model, ...)

  ## S3 method for class 'drc'
hatvalues(model, ...)

Arguments

model

an object of class 'drc'.

...

additional arguments (not used).

Details

Hat values and Cook's distance are calculated using the formula given by Cook et al. (1986) and McCullagh and Nelder (1989).

The output values can be assessed in the same way as in linear regression.

Value

A vector of leverage values (hat values) or values of Cook's distance (one value per observation).

Author(s)

Christian Ritz

References

Cook, R. D. and Tsai, C.-L. and Wei, B. C. (1986) Bias in Nonlinear Regression, Biometrika 73, 615–623.

McCullagh, P. and Nelder, J. A. (1989) emphGeneralized Linear Models, Second edition, Chapman \& Hall/CRC.

Examples

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ryegrass.LL.4 <- drm(rootl ~ conc, data = ryegrass, fct = LL.4())

hatvalues(ryegrass.LL.4)

cooks.distance(ryegrass.LL.4)

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