[R] logit regression, test among groups
Martin Henry H. Stevens
HStevens at muohio.edu
Tue May 28 12:59:23 CEST 2002
My logistic regression model includes one qualitative and one quantitative
aes <- glm(p.a ~ spp * log(light), family=binomial(link=logit)),
where spp is abundance of 3 species and light is subcanopy light
availability varying from 0 1.
I want to test differences among levels of the quantitative variable at a
value of x other than the current log(light)=0. I tried using
I(log(light+.5)) but this caused serious lack of fit (AIC went from 1574 to
1656, and diagnostic plots demonstrated poor fit). How would create a model
statement such that I test differences among groups at log(light)=approx. 2?
Martin Henry H. Stevens, Assistant Professor
338 Pearson Hall
Oxford, OH 45056
Office: (513) 529-4206
Lab: (513) 529-4262
FAX: (513) 529-4243
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