On Sat, 8 Sep 2001 menstav@hotmail.com wrote:
> Full_Name: Menelaos Stavrinides
> Version: 1.3. 1
> OS: Windows 98
> Submission from: (NULL) (193.129.76.90)
>
>
> When model simplification is used in glm (binomial errors) and anova is
used two
> compare two competitive models one can use either an "F" or a
"Chi" test.
>
> R always performs an F test (Although when test="Chi" the test is
labeled as
> Chi, there isn't any difference between F and Chi test)
>
> Let us assume model1 and model2, where model2 a simplified version of
model1
>
> model1_glm(y~factor1*factor2,binomial)
> model2_update(model1,~.-factor2)
> anova(model1,model2,test="F")# will give the same result as
> anova(model1,model2,test="Chi")
See help(family) and help(anova.glm). For a binomial family the scale
estimate in the F test is fixed at one, so they should be the same.
If you want extimates scale, use a quasibinomial family.
This applies to PR#1087 too.
Please do read the section of BUGS in the FAQ.
--
Brian D. Ripley, ripley@stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272860 (secr)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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