How to Minimize Maximum Regret in Repeated Decision-Making

Consider repeated decision making in a stationary noisy environment given a …nite set of actions in each round. Payo¤s belong to a known bounded interval. A rule or strategy attains minimax regret if it minimizes over all rules the maximum over all payo¤ distributions of the di¤erence between achievable and achieved discounted expected payo¤s. Linear rules that attain minimax regret are shown to exist and are optimal for a Bayesian decision-maker endowed with the prior where learning is most di¢ cult. Minimax regret behavior for choosing between two actions given small or intermediate discount factors is derived and only requires two rounds of memory. JEL classi…cation: D81, D83.