3rd International Symposium on
Imprecise Probabilities and Their Applications

ISIPTA '03

University of Lugano
Lugano, Switzerland
14-17 July 2003

ELECTRONIC PROCEEDINGS

Thomas Augustin

On the Suboptimality of the Generalized Bayes Rule and Robust Bayesian Procedures from the Decision Theoretic Point of View --- a Cautionary Note on Updating Imprecise Priors

Abstract

This paper discusses fundamental aspects of inference with imprecise probabilities from the decision theoretic point of view. It is shown why the equivalence of prior risk and posterior loss, well known from classical Bayesian statistics, is no longer valid under imprecise priors. As a consequence, straightforward updating, as suggested by Walley's Generalized Bayes Rule or as usually done in the Robust Bayesian setting, may lead to suboptimal decision functions. As a result, it must be warned that, in the framework of imprecise probabilities, updating and optimal decision making do no longer coincide.

Keywords. Decision making, generalized risk, generalized expected loss, imprecise prior risk and posterior loss, robust Bayesian analysis, Generalized Bayes rule

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Authors addresses:

Ludwigstr. 33
D-80539 Munich
Germany

E-mail addresses:

Thomas Augustin thomas@stat.uni-muenchen.de

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