From bolker@zoo.ufl.edu  Mon Jan 27 18:50:04 2003
From: bolker@zoo.ufl.edu (Ben Bolker)
Date: Mon Jan 27 18:50:04 2003
Subject: [Rd] help page for anova.glm/variation between S-PLUS and R behavior
Message-ID: <Pine.LNX.4.44.0301271249080.17354-100000@bolker.zoo.ufl.edu>

   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