Model diagnostics for nonlinear dose-response models

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

Usage

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

Arguments

model: an object of class 'drc'.
...: additional arguments (not used).

Value

A vector of leverage values (hat values), one value per observation.

Details

Hat values 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.

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) Generalized Linear Models, Second edition, Chapman & Hall/CRC.

Author

Christian Ritz

Examples

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

hatvalues(ryegrass.LL.4)
#>          1          2          3          4          5          6          7 
#> 0.13332342 0.13332342 0.13332342 0.13332342 0.13332342 0.13332342 0.09539668 
#>          8          9         10         11         12         13         14 
#> 0.09539668 0.09539668 0.27948291 0.27948291 0.27948291 0.28191831 0.28191831 
#>         15         16         17         18         19         20         21 
#> 0.28191831 0.12467564 0.12467564 0.12467564 0.12949336 0.12949336 0.12949336 
#>         22         23         24 
#> 0.15571960 0.15571960 0.15571960