[R-sig-ME] prior specification in MCMCglmm

[Celine Teplitsky]

Dear all,

I realise that Jarrod is doing field work, but I'm really hoping someone 
can answer my question while he's not around.

I am running animal models estimating covariances between life history 
traits, and I'm having trouble knowing which prior to use.

Thing is, if I use a prior as described on the Wam wiki site with 
V=PhenotypicVar/4 (as I have 3 random effects + residual), I have very 
nice results, with some significant genetic correlations between some 
life history traits.

However, one reviewer asked about prior sensitivity because CI were 
pretty large, so I went back to MCMCglmm course notes and saw that non 
informative prior were supposed to be V=diag(nbDimV)*0 and n=nbDimV-3. 
This led to an error message about G being ill conditioned, so I tried 
with diag(nbDimV)*0.001 and diag(nbDimV)*0.01 instead of diag(nbDimV)*0, 
and diag(nbDimV)*0.01 worked... But then I have the posterior of 
additive genetic variance collapsing on 0 for some trait. So my guess 
would be that I should use those latest priors, and believe my nice 
results did not exist. But as Hadfield et al paper and the Wam wiki 
website do not recommend those priors, I am a bit confused. Could 
someone help me figure out what would be the right thing to do?

All my apologies if this is a silly question, but I'm feeling a bit lost 
here

Thanks a lot in advance

Celine

-- 

Celine Teplitsky
Département Ecologie et Gestion de la Biodiversité UMR 7204
Unité Conservation des Espèces, Restauration et Suivi des Populations
Case Postale 51
55 rue Buffon 75005 Paris

Webpage : http://www2.mnhn.fr/cersp/spip.php?rubrique96
Fax : (33-1)-4079-3835
Phone: (33-1)-4079-3443