Compute Models by Adding One Term

add1

Description

Returns information on models that include one more term than the given object.

This function is an S Version 3 generic. (See Methods.) Method functions can be written to handle specific S Version 3 classes of data. Classes that have methods for this function include lm, glm and mlm.

The default method is described here.

Usage

add1(object, scope, ...)
## Default S3 method:
add1(object, scope, scale = 0, test = c("none", "Chisq"), k = 2, ...)

Arguments

object	a fitted model. It must be of a class such that formula(object) extracts its formula and extractAIC(object) computes the number of estimated parameters and its AIC statistic.
scope	a description of the range of new terms to add. Generally scope is either a formula or a character vector of term labels. If it is a formula, it should include all the terms in the original model (or a dot, which represents them) as well as the terms to add. All terms that do not violate marginality rules are added. (For example, x:y are added only if both x and y are in the original model).
...	other arguments depend on the method used.

Details

The main default method is add1.default, which produces an anova object. Other kinds of models could use different methods for summarizing the additional fits and, possibly, different classes of objects to represent the result.

Other methods are add1.lm, add1.glm and add1.mlm.

Value

returns an anova object containing at least the number of degrees of freedom in the test fit and the AIC for the fit. There can be other columns, depending on the class of the object and the test requested.

References

Chambers, J. M. and Hastie, T .J. (Eds.) 1992. Statistical Models in S. Pacific Grove, CA.: Wadsworth & Brooks/Cole. Chapter 4.