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McSim query

From: Suhrid Balakrishnan
Subject: McSim query
Date: Fri, 25 Oct 2002 02:46:42 -0400 (EDT)


I'm trying to do some analysis with McSim 4.1 and I'd like to specify
priors in a heirarchical fashion exactly as the authors of the software
did in their 1996 paper - Bois, F. Y., Gelman, A., Jiang, J., Maszle, D.,
Zeise, L. and Alexeef, G. (1996). Population toxicokinetics of
tetrachloroethylene. Archives of Toxicology 70:347-355. also used in
Gelman, A., Bois, F. Y. and Jiang, J. (1996). Physiological
pharmacokinetic analysis using population modeling and informative prior
distributions. Journal of the American Statistical Association

The problem I'm facing is that I see no way to easily incorporate the
Lognormal hierarchical prior (mu*, Sigma*) (where mu* and Sigma* are the
geometric mean and standard deviations respectively = exp(mu) and
exp(Sigma)) with further conditional distributions on mu ~ Normal (M,S)
and Sigma as inverse-gamma(a,b) (a, b being the shape and scale
parameters, respectively) in the McSim framework. 

I've tried a number of things including toying with levels, exponents,
outputs, scaling etc. and nothing seems to work.

What one desires, I presume, is a way to specify the following
hierarchical distributions in the simulation file (which the authors used
in both references above):

Distrib (Sigma_V, InvGamma, 2, 0.1823);
Distrib (Mean_V, Normal, 0.1, 1.2); # values are abitrary
Distrib (V, TruncLogNormal, exp(Mean_V), exp(Sigma_V), 1e-6,10);

But the above formulation isn't allowed by McSim (no exponentiation
alllowed in the Distrib specification).

Or an alternative way to get the same effect - is there something obvious
that I'm not seeing? Presumably, there is a way to do this, I would be
greatly appreciative if anyone would let me know how.

Thanks in advance,



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