[R] Q about how to use Anova.mlm

[John Fox]

Dear Paul,

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On
> Behalf Of pgseye
> Sent: January-29-09 10:07 PM
> To: r-help at r-project.org
> Subject: Re: [R] Q about how to use Anova.mlm
> 
> 
> Thanks a lot for that John - really helpful. I generated some random
numbers
> and seem to be able to get it to work, so that's great.
> 
> One thing - it's come up with a 'Type III' test and given me a few
warnings.
> What's the difference between Type II and Type III tests (if there's some
> basic guide you can point me to).

The default for Anova() is "type-II" tests, but the computational approach
taken doesn't provide a test for the intercept, which is the only
between-subject term in the model; thus, a "type-III" test is substituted.
In a model with only an intercept, there is no distinction between the two
"types" of tests.

More generally, types II and III tests address different hypotheses in
models in which some terms are marginal to others. There's a brief
explanation in my R and S-PLUS Companion to Applied Regression (Wiley,
2002), which is the book associated with the car package in which Anova()
resides. There's a more complete discussion in my Applied Regression
Analysis and Generalized Linear Models, Second Edition (Sage, 2008). Neither
book, BTW, discusses repeated-measures models.

I hope this helps,
 John

> 
> Thank you again.
> 
> Best,
> 
> Paul
> 
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