[R-sig-eco] GEE and AIC

[Simon Blomberg]

See Pan (2001). Akaike's information criterion in generalized estimating
equations. Biometrics 57: 120-125. See also the book by Hardin and Hilbe
2003 for examples and applications.

The only reason to jump to gee is if your dependent variable is not
Gaussian (but is an exponential family, e.g. binomial, Poisson, etc.),
and you have several covariates, some of which may be continuous. 

You should be careful with your model of evolution if your dependent
variable is non-Gaussian. Brownian motion cannot apply to discrete
variables. Instead, a discrete-state, continuous time Markov model might
be more appropriate, in which case you can't directly use the shared
branch-lengths of the phylogeny as estimates of phylogenetic covariance.
See Martins and Hansen 1997 Phylogenies and the comparative method: a
general approach to incorporating phylogenetic information into the
analysis of interspecific data. American Naturalist 149:646–667.
Erratum 153:448. Tony Ives and Ted Garland have submitted a manuscript
on this topic, but you will have to contact them for further info. The
sample size has little to do with the issue, although fitting gee models
with small sample sizes can be extremely difficult. There are also
formidable problems with bias in the parameter estimates.

I've cc'ed this to r-sig-phylo, which is probably a better forum for
discussing comparative analyses.

Cheers,

Simon.


 Thu, 2008-05-29 at 15:50 -0700, BriAnne Addison wrote:
> This is tangential to the previous string.
> 
> Has anyone calculated (pseudo)AIC values for generalized estimation 
> equations in the GEE package (or related packages)?  I wish to compare 
> among several models where the data are not phylogenetically 
> independent.  I plan to use GEE to account for my phylogeny, rather 
> than conventional contrast values, because I have a relatively small 
> sample size and a variety of continuous and multilevel discrete 
> factors.  The statistical problem is analogous to data which is 
> spatially autocorrelated.  Thoughts?
> 
> Thanks,
> BriAnne
> 
> 
> 
> 
> 
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> BriAnne Addison
> Ecology, Evolution and Systematics
> Biology Department
> University of Missouri - St Louis
> 
> brianne.addison at umsl.edu
> 
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-- 
Simon Blomberg, BSc (Hons), PhD, MAppStat. 
Lecturer and Consultant Statistician 
Faculty of Biological and Chemical Sciences 
The University of Queensland 
St. Lucia Queensland 4072 
Australia
Room 320 Goddard Building (8)
T: +61 7 3365 2506
http://www.uq.edu.au/~uqsblomb
email: S.Blomberg1_at_uq.edu.au

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The combination of some data and an aching desire for 
an answer does not ensure that a reasonable answer can 
be extracted from a given body of data. - John Tukey.