Re: [R] lmm WITHOUT random factor (lme4)

From: Mark Difford <mark_difford_at_yahoo.co.uk>
Date: Thu, 17 Mar 2011 02:54:43 -0700 (PDT)

On Mar 17, 2011; 11:43am Baugh wrote:

>> Question: can I simply substitute a dummy var (e.g. populated by zeros)
>> for "ID" to run the model
>> without the random factor? when I try this R returns values that seem
>> reasonable, but I want to be sure
>> this is appropriate.

If you can fit the model using lme (and it looks like you easily can) then another check would be:

## Compare models with and without random effects fm <- lm(Reaction ~ Days, sleepstudy)
fm1 <- lme(Reaction ~ Days, random= ~1|Subject, sleepstudy)

anova(fm1, fm)                 ## lme-fitted model must come first

Regards, Mark.

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