Error in factor.scope(ffac, list(add = fadd, drop = fdrop)) :
upper scope does not include modelJust because R internally decides to order terms differently than in the scope (this may happen even when you have produced the scope by first fitting the maximal model, and then extracting that using scope=formula()). I once was diligent enough to trace this to a certain C function where this ordering was done, but I was not clever enough to instantly know how to change the behaviour.
cheers, jari oksanen
On 19 Mar 2004, at 17:25, Anon. wrote:
I can only assume I'm betraying my ignorance here, but this is not what I would expect.
I'm getting the following from a stepwise selection (with both step and stepAIC):
> step(lm(sqrt(Grids)~ SE + Edge + NH), scope=~ (Edge + SE + NH)^2) Start: AIC= 593.56 sqrt(Grids) ~ SE + Edge + NH
Df Sum of Sq RSS AIC <none> 2147.0 593.6 + Edge:NH 1 3.0 2143.9 595.1 + SE:NH 4 23.2 2123.8 598.4 - NH 1 75.8 2222.8 601.6 - Edge 1 448.7 2595.7 646.4 - SE 4 1033.7 3180.6 699.1
My problem is that the SE:Edge term is not added. Now, I know that I've specified the terms in a different order in the start model and the scope, but this shouldn't matter, should it? Aren't these model specifications commutative?
Am I missing something important, or is this just an obscure feature?
Bob
-- Bob O'Hara
Dept. of Mathematics and Statistics P.O. Box 4 (Yliopistonkatu 5) FIN-00014 University of Helsinki Finland Telephone: +358-9-191 23743 Mobile: +358 50 599 0540 Fax: +358-9-191 22 779 WWW: http://www.RNI.Helsinki.FI/~boh/ Journal of Negative Results - EEB: http://www.jnr-eeb.org
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