Doug,

Test fixed effects by single term in anova() and test by likelihood ratio test are different. In anova you are assuming that random effects estimates are the parametric values, in other words, this test is conditional to the random effects.

When you want to test fixed effects by double term in anova (anova(m1, m0)) you must use maximum likelihood (lmer(y~x1+x2+(1|x3), REML=FALSE)). It's because REML is based in function of the fixed effects and ML not.

Using "1" in your simple model means adjust to the general mean.

At your disposal.
Walmes Zeviani, Lavras, MG - Brasil.




________________________________
De: Doug Adams <fog0@gmx.com>

ac.uk; R sig-mixed-models <r-sig-mixed-models@r-project.org>
Enviadas: Quarta-feira, 10 de Fevereiro de 2010 3:06:27
Assunto: Re: [R-sig-ME] anova on lmer object

On Tue, Feb 9, 2010 at 4:32 PM, Doug Adams <fog0@gmx.com> wrote:
[[elided Yahoo spam]]
>

If I only pass one model into the anova function, does it assume the
nested model being tested against is the one without fixed effects?

And are the denominator degrees of freedom the ones listed in the output table:
         Df Sum Sq Mean Sq F value
division  2 103.59  51.793  1.0155

If it's 2, am I correct in thinking that it's because my fixed effect
has 3 states, the first of which would be considered the baseline
against which the others are offset -- so it would exist in the model
without fixed effects?  (So the baseline, and then the other 2
additional states for fixed effects...)

One more question:  If I want to explicitly spell out the simpler
model that doesn't have fixed effects so I can test for them, would
this be correct:
Complete Model:        lmer(outcome ~ FixedEffect + (1|RandomGrouping), data...)
Simplified Model:        lmer(outcome ~ 1 + (1|RandomGrouping))

so that "1" is like a placeholder for the first level?

Goodness, thanks everyone for your patience with my endless questions.



      ____________________________________________________________________________________
[[elided Yahoo spam]]

	[[alternative HTML version deleted]]


