Dear BUGS users,
A commonly used "non informative prior" for a normal variance is
tau ~ dgamma(0.001,0.001)
I believe the reason is that a gamma pdf approximates an inverse
distribution when parameters are taken very small.
The problem :
I have a model with such a prior
tau ~ dgamma(0.001,0.001) ;
var <- 1/tau ;
on the precision, which is running without any problem under WinBUGS13. But
this model doesn't run under the updated version WinBUGS14 (trap message :
"unable to bracket slice for node tau").
My questions :
1) Does the updated 1.4 version use other sampling methods as 1.3 ?.
2) The model is running under 1.4 with the following code :
var ~ dgamma(0.001,0.001) ;
tau ~ 1/var ;
To my mind, assigning a prior pdf =1/V on the Variance V is the same than
assigning a prior pdf =1/Tau on the precision Tau. Thus, is this second
solution wrong ?.
3) Is it better to use something like
log.tau ~ dunif(-10,10) ;
tau <- exp(log.tau) ?
Thanks for your help !
Best,
Etienne
Etienne RIVOT
*********************************************************************
Etudiant en these / Ph.D. Student
UMR Ecobiologie et Qualite des Hydrosystemes continentaux
Institut National de la Recherche Agronomique
65, rue de St Brieuc, CS 84215, 35042 Rennes cedex, FRANCE
Tel : +33 2 23 48 54 49 ; Fax : +33 2 23 48 54 40
Email : [log in to unmask]
Internet : http://www.rennes.inra.fr/
*********************************************************************
-------------------------------------------------------------------
This list is for discussion of modelling issues and the BUGS software.
For help with crashes and error messages, first mail [log in to unmask]
To mail the BUGS list, mail to [log in to unmask]
Before mailing, please check the archive at www.jiscmail.ac.uk/lists/bugs.html
Please do not mail attachments to the list.
To leave the BUGS list, send LEAVE BUGS to [log in to unmask]
If this fails, mail [log in to unmask], NOT the whole list
