Dear mixed model list serve group,

I was wondering if anyone could advise me on the significance testing of
random effects in a generalized linear mixed model? I am a biologist with
basic statistical knowledge and since I am using a complex method, I want
to make sure that I am doing things correctly.

My experiment:
I performed a paternal half-sib breeding design to examine whether a
variety of mating and non-mating behaviors are significantly heritable. I
am interested in whether "sire" explains a significant amount of the
behavioral variation.

My analysis:
The behavioral data was non-normal and had a lot of zeros, so I decided to
try a GLMM. I conducted my analysis in SAS GLIMMIX with sire and dam(sire)
as random effects and no fixed effects. I specified a negative binomial
distribution with a log link function and used the Laplace approximation to
get a true log-likelihood.

My question:
When I want to figure out whether my random effect of sire is significant,
do I compare models with and without the sire effect in their -2 log
likelihoods under the "Fit Statistics" or the -2 log likelihood (behavior |
random effects) under the "Fit Statistics for conditional distribution"?
Both of these things are included in the SAS output.

I am confused because I have seen some statistics papers (way over my head
so I may be totally off-base here, e.g.Paul and Deng 2000) that suggest
using the conditional distributions for sparse data (which mine is). I have
also analyzed my zero-rich data as binomial (scored as 1/0, binomial
distribution, probit link function, laplace estimation) which seems much
more appropriate and the conclusions in terms of the significance of sire
match better with those from the log likelihood tests using the conditional
distribution than the regular log likelihood test from the marginal
distribution.

I apologize if this is super obvious but I have searched SAS
discussions,etc and as of yet, I can find no straightforward answer. I
would appreciate any help you could offer!

Thank you!

Sincerely,

Katie

-- 
---- ><((((º> ----------- ><((((º> ----

Katie E. McGhee

Postdoctoral Fellow
Integrative Biology
University of Illinois
433 Morrill Hall
505 S. Goodwin Ave.
Urbana, IL, 61801

kemcghee@illinois.edu

	[[alternative HTML version deleted]]


