[R-sig-ME] how reliable are inferences drawn from binomial modelsfor small datasets fitted with lme4?
David Duffy
David.Duffy at qimr.edu.au
Mon Jul 6 07:38:44 CEST 2009
On Sun, 5 Jul 2009, Roger Levy wrote:
> This post may be of interest in light of the recent discussion of PQL versus
> Laplace-approximated likelihood. I'm facing an interestingly challenging
> analysis of a relatively small (190-observation) binary-response dataset with
> a single two-level treatment and two crossed random factors (call them F1 and
> F2). The question of current interest is whether I can infer a difference in
> fixed effect of treatment ... [SNIP]
Although F1 has an effect, F2 doesn't seem as impressive:
For Response, Tarone score test for extrabinomial variance gives
F1 3.86 (P=0.0493), F2 0.54 (P=0.4616).
So it seems reasonable just to ignore F2. Then the conditional logistic
regression stratifying on F1 is nicely significant:
clogit(Response ~ Treatment + strata(F1), method="exact", data = x)
coef exp(coef) se(coef) z p
Treatment2 2.73 15.3 1.10 2.49 0.013
Likelihood ratio test=10.9 on 1 df, p=0.000957 n= 190
(and equivalent score test 9.054, P=0.0026).
The conditional logistic should be fairly robust, and at least
gives some kind of benchmark for other models.
Cheers, 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 \_,-._/
| 300 Herston Rd, Brisbane, Queensland 4029, Australia GPG 4D0B994A v
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