Redoing the foundations of decision theory: Decision theory with subjective states and outcomes

Speaker:	Professor Joe HALPERN
		Computer Science Department
		Cornell University

Title:		"Redoing the foundations of decision theory: Decision
		 theory with subjective states and outcomes"

Date:		Tuesday, 7 August 2007

Time:		11:00 am - 12 noon

Venue:		Room 3530 (via lift nos. 25/26), HKUST

Abstract:

The standard approach in decision theory (going back to Savage) is to
place a preference order on acts, where an act is a function from states
to outcomes.   If the preference order satisfies appropriate postulates,
then the decision maker can be viewed as acting as if he has a probability
on states and a utility function on outcomes, and is maximizing expected
utility.  This framework implicitly assumes that the decision maker knows
what the states and outcomes are.  That isn't reasonable in a complex
situation.  For example, in trying to decide whether or not to attack
Iraq, what are the states and what are the outcomes?  We redo Savage
viewing acts essentially as syntactic programs.  We don't need to assume
either states or outcomes.   However, among other things, we can get
representation theorems in the spirit of Savage's theorems; for Savage,
the agent's probability and utility are subjective; for us, in addition to
the probability and utility being subjective, so is the state space and
the outcome space.  I discuss the benefits, both conceptual and pragmatic,
of this approach.  As I show, among other things, it provides an elegant
solution to framing problems.

This is joint work with Larry Blume and David Easley.  No prior knowledge
of Savage's work is assumed.

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Biography:

Joseph Y. HALPERN received a B.Sc. in mathematics from the University of
Toronto in 1975 and a Ph.D. in mathematics from Harvard in 1981.  In
between, he spent two years as the head of the Mathematics Department at
Bawku Secondary School, in Ghana.  He is currently a professor of computer
science at Cornell University, where he moved in 1996 after spending 14
years at the IBM Almaden Research Center.

Joseph's interests include reasoning about knowledge and uncertainty,
decision theory and game theory, fault-tolerant distributed computing,
causality, and security. Together with his former student, Yoram Moses, he
pioneered the approach of applying reasoning about knowledge to analysing
distributed protocols and multi-agent systems; he won a Godel Prize for
this work.  He received the Publishers' Prize for Best Paper at at the
International Joint Conference on Artificial Intelligence in 1985 (joint
with Ronald Fagin) and in 1989, and the Reiter Prize for best paper at the
Conference on Knowledge Representation and Reasoning in 2006 (joint with
Larry Blume and David Easley).  He has coauthored 6 patents, two books
("Reasoning About Knowledge" and "Reasoning About Uncertainty"), over 100
journal publications, and over 150 conference publications. He is a former
editor-in-chief of the Journal of the ACM, a Fellow of the ACM, the AAAI,
and the AAAS, and was the recipient of a Guggenheim and a Fulbright
Fellowship.