add1 in glm

On Tue, 5 Nov 2002, Murray Jorgensen wrote:

I'm having a bit of difficulty using the stepwise model-building tools
in a glm context. Here, for example is one problem I have had using
add1, where the abbreviation "." does not work as I expected it to do. I

What did you expect?  `.' means `what is already there' in updating a
formula, so you asked for nothing to be added.  The help page says

   scope: a formula giving the terms to be considered for adding or
          dropping.

and that seems precise to me.

Well I based it on my interpretation of the beginning of the first 
example in the V&R discussion, also the first example in the stepAIC() page:

data(quine)
quine.hi <- aov(log(Days + 2.5) ~ .^4, quine)

This seemed to suggest that "." meant "all the predictors". Now that I 
know what "." means, my error is clear.

Does anyone know of  functions for adding the best single term (or 
dropping the worst) from a specified scope? (Respecting marginality, of 
course!)

Murray









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