[R-sig-ME] Significance and lmer

[David Duffy]

On Sat, 27 Mar 2010, Adam D. I. Kramer wrote:
> On Sat, 27 Mar 2010, Ben Bolker wrote:
>
>>> ...a significant result completely unrelated to the t-value. My
>>> interpretation of this would be that we have no good evidence that the
>>> estimate for 'pred' is nonzero, but including pred in the model improves
>>> prediction.
>> 
>
>>  I have seen some wonky stuff happen with update() [sorry, can't provide
>> any reproducible details], I would definitely try fitting b by spelling
>> out the full model rather than using update() and see if that makes a
>> difference.
>
> This produces no difference in b's estimates or the anova() statistics.
> (That said, I originally was fitting [implicitly] with REML=TRUE, which did
> make a difference, but not a big one).

The two models both have the same number of observations, one hopes?  How 
many observations per studyID and how many studyIDs?

> Well, thanks for the reply. Are you, then, of the opinion that the above
> interpretation is reasonable?

I would be a bit nervous.  My interpretation would be that the model is 
inappropriate for the data (as the Wald and LR tests should roughly agree 
for a LMM, as Ben pointed out), and would look at diagnostic plots of 
residuals etc.  The bunch of zeroes you mention may still be stuffing 
things up ;)  Is a left-censored model plausible?

Just my 2c, David Duffy.

-- 
| David Duffy (MBBS PhD)                                         ,-_|\
| email: davidD at qimr.edu.au  ph: INT+61+7+3362-0217 fax: -0101  /     *
| Epidemiology Unit, Queensland Institute of Medical Research   \_,-._/
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