Re: [R] strange results from binomial lmer?

From: Henric Nilsson (Public) <nilsson.henric_at_gmail.com>
Date: Fri, 14 Mar 2008 02:36:00 +0100

johnson4_at_babel.ling.upenn.edu wrote:

> I'm running lmer repeatedly on artificial data with two fixed factors (called
> 'gender' and 'stress') and one random factor ('speaker'). Gender is a
> between-speaker variable, stress is a within-speaker variable, if that matters.
> Each dataset has 100 rows from each of 20 speakers, 2000 rows in all.
>
> About 5% of the time I get a strange result, where the lmer() model with BOTH
> fixed factors and the random factor ('gs_s') comes out MUCH worse compared to
> the models with ONE fixed factor and the random factor ('g_s' and 's_s'), and
> also compared to the glm() model with both fixed factors and no random factor
> ('gs').
>
> This doesn't make much sense to me.
>
> I've placed a dataset on the Web that exhibits this behavior, as follows:
>
> dat <- read.csv("http://www.ling.upenn.edu/~johnson4/strange.csv")
>
> gs <- glm(outcome~gender+stress,binomial,dat)
> g_s <- lmer(outcome~gender+(1|speaker),dat,binomial)
> s_s <- lmer(outcome~stress+(1|speaker),dat,binomial)
> gs_s <- lmer(outcome~gender+stress+(1|speaker),dat,binomial)
>
> logLik(gs) # -1344 (df=3)
> logLik(g_s) # -1342 (df=3)
> logLik(s_s) # -1314 (df=3)
> logLik(gs_s) # -11823 (df=4)
>
> This seems like an error of some kind. The glm() model with both fixed effects
> is well-behaved, but lmer() seems to be going haywire when confronted with the
> same situation plus the random effect.

What version of the `lme4' package are you using? (Including the output of `sessionInfo()' would have helped here, as suggested by the posting guide.)

Using version 0.999375-8 of the `lme4' package, I get

 > logLik(gs) # -1344 (df=3)
'log Lik.' -1344.320 (df=3)
 > logLik(g_s) # -1342 (df=3)
'log Lik.' -1341.794 (df=3)
 > logLik(s_s) # -1314 (df=3)
'log Lik.' -1314.395 (df=3)
 > logLik(gs_s) # -11823 (df=4)
'log Lik.' -1312.270 (df=4)

>
> Could anyone advise me how to stop this from happening, and/or explain why it
> is?

You're likely using some obsolete version of `lme4'. Try downloading a development snapshot from R-Forge
(http://r-forge.r-project.org/projects/lme4/).

HTH,
Henric

>
> Thanks very much,
> Daniel
>
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>



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https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. Received on Fri 14 Mar 2008 - 01:39:10 GMT

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