Compute Models by Adding One Term - Generic Function
DESCRIPTION:
Returns information on models that have one more term than the given object.

This function is generic (see Methods); method functions can be written to handle specific classes of data. Classes which already have methods for this function include: lm.

USAGE: 
add1(object, scope, ...)
REQUIRED ARGUMENTS:
object:
a fitted model, which in some sense represents some but not all possible terms.
scope:
a description of the range of new terms to add. In the case of linear models and related models, this is given by a formula.
VALUE:
an object representing some or all of the information got by fitting each of the models formed by adding a term from scope to the original model in object.
DETAILS:
The main (currently only) method for this is add1.lm, 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.
SEE ALSO:
add1.lm , drop1 , glm , step .
EXAMPLES: 
# consider all interactions of terms in lm.object for inclusion
add1(lm.object, ~ .^2)


glm.object <- glm(Kyphosis ~ bs(Start, 5) + Number, family = binomial,
                  data = kyphosis)
# try some candidate transformations for Age.
add1(glm.object, ~ . -Age + poly(Age,2) + log(Age) + sqrt(Age))