Bayesian rationality is the paradigm of rational behavior in neoclassical economics. A rational agent in an economic model is one who maximizes her subjective expected utility and consistently revises her beliefs according to Bayes's rule. The paper raises the question of how, when and why this characterization of rationality came to be endorsed by mainstream economists. Though no definitive answer is provided, it is argued that the question is far from trivial and of great historiographic importance. The story begins with Abraham Wald's behaviorist approach to statistics and culminates with Leonard J. Savage's elaboration of subjective expected utility theory in his 1954 classic The Foundations of Statistics. It is the latter's acknowledged fiasco to achieve its planned goal, the reinterpretation of traditional inferential techniques along subjectivist and behaviorist lines, which raises the puzzle of how a failed project in statistics could turn into such a tremendous hit in economics. A couple of tentative answers are also offered, involving the role of the consistency requirement in neoclassical analysis and the impact of the postwar transformation of US business schools.Word count: 19,618 (including footnotes and references) JEL Codes: B21, B31, D81 Keywords: Savage, Wald, rational behavior, Bayesian decision theory, subjective probability, minimax rule, statistical decision functions, neoclassical economics * Via Curtatone e Montanara 15, 56126, Pisa, Italy; giocoli@mail.jus.unipi.it. I thank for their useful comments and suggestions Marcello Basili, Marco Dardi, Gur Huberman, Philippe Mongin, Ivan Moscati, Carlo Zappia. I am also grateful to the organizer, Samuel Ferey, and the participants to the Symposium on "Decision theory in economics: between logic and psychology" held during CLMPS 2011 in Nancy (France). The financial support of MIUR PRIN "Mathematics in the history of economics" is gratefully acknowledged. The usual disclaimers apply.
1From Wald to Savage: homo economicus becomes a Bayesian statistician Nicola Giocoli *
Department of Economics, University of Pisa
IntroductionRational behavior is the cornerstone of neoclassical economics. In the specific case of decisions under uncertainty, an agent can be termed rational if and only if she behaves as a Bayesian decision-maker, that is to say, if she makes choices according to the three main tenets of Bayesianism, namely, if she i) captures uncertainty by probability (whenever a fact is not known, the decision-maker should have probabilistic beliefs about it); ii) captures information by conditioning probabilities (the decision-maker should update her prior beliefs according to Bayes's rule as new information arrives); iii) follows the expected utility rule (the chosen alternative should maximize the weighted average of probabilities and utilities). In short, in the neoclassical paradigm economic rationality coincides with Bayesian rationality, as embodied in standard game and decision theory. 1 Yet, exactly how, when and why did the traditional no...