From bolker@zoo.ufl.edu  Mon Jan 27 19:27:03 2003
From: bolker@zoo.ufl.edu (Ben Bolker)
Date: Mon Jan 27 19:27:03 2003
Subject: [Rd] help page for anova.glm/variation between S-PLUS and R
 behavior
In-Reply-To: <Pine.LNX.4.44.0301271804320.17520-100000@gannet.stats>
Message-ID: <Pine.LNX.4.44.0301271330110.18915-100000@bolker.zoo.ufl.edu>

  OK, then, what about adding a note to section 3.3.3 (Other differences
between R and S-PLUS) of the R FAQ ?  I just want to minimize confusion 
for people crossing over -- at least point to the fact that S-PLUS handles 
it differently.

  Ben

On Mon, 27 Jan 2003 ripley@stats.ox.ac.uk wrote:

> Not really!
> 
> I don't think it is our job to describe the inconsistencies of S-PLUS,
> especially since that might change from version to version. It would be
> really messy, as S-PLUS ignores the scale for the Chisq test (which seems
> perverse), and lacks the dispersion argument.
> 
> On Mon, 27 Jan 2003, Ben Bolker wrote:
> 
> > 
> >    When using test="F" in stat.anova() / anova.glm(), R uses the assumed 
> > dispersion parameter for the specified family (e.g. scale=1 for binomial), 
> > while S-PLUS automatically uses the estimated dispersion parameter 
> > (residual deviance/residual df).  I think there are good reasons for the 
> > behavior in R -- it fits with the "you get what you actually asked for" 
> > philosophy -- and there are hints in the documentation (anova.glm(): "for 
> > [models] with dispersion estimated by moments ... the F test is most 
> > appropriate"; family/binomial(): "The behaviour of S-PLUS is closer to the 
> > quasi- variants").
> >    Would R-core consider it reasonable to add yet another sentence to the
> > anova.glm() documentation, e.g. after the "... F test is most appropriate"  
> > sentence above, adding: "(Note: unlike R, S-PLUS automatically uses the
> > moment-estimated dispersion for F-tests even for the binomial and Poisson
> > families:  see ?quasibinomial.)"  ?
> > 
> >   Ben Bolker
> > 
> > 
> 
> 

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[Rd] help page for anova.glm/variation between S-PLUS and R behavior
Ben Bolker