drc (version 1.6-1)

modelFit: Checking the model fot

Description

Checking the fit of dose-response model by means of formal lack-of-fit tests or graphical procedures.

Usage

modelFit(object, test = NULL, method = c("gof", "cum"))

Arguments

object

object of class 'drc'

test

character string defining the test method to apply

method

character string specifying the method to be used for assessing the model fit

Value

• An object of class 'anova' which will be displayed in much the same way as an ordinary ANOVA table.

Details

Currently two methods are available. For continuous data the clasical lack-of-fit test is applied (Bates and Watts, 1988). The test compares the dose-response model to a more general ANOVA model using an approximate F-test. For quantal data the crude goodness-of-fit test based on Pearson's statistic is used. None of these tests are very powerful. A significant test result is more alarming than a non-significant one. More methods will become available in the future.

References

Bates, D. M. and Watts, D. G. (1988) Nonlinear Regression Analysis and Its Applications, New York: Wiley & Sons (pp. 103--104).

Examples

## Comparing the four-parameter log-logistic model to a one-way ANOVA model using an approximate F test
## in other words applying a lack-of-fit test
ryegrass.m1 <- drm(rootl ~ conc, data = ryegrass, fct = W1.4())
modelFit(ryegrass.m1)