The 2009 Lawrence R. Klein lecture: Diversified treatment under ambiguity

This article develops a broad theme about treatment under ambiguity through study of a particular decision criterion. The broad theme is that a planner may want to cope with ambiguity by diversification, assigning observationally identical persons to different treatments. Study of the minimax-regret (MR) criterion substantiates the theme. The article significantly extends my earlier analysis of one-period planning with an individualistic treatment and a linear welfare function. I show that MR treatment allocations are fractional in a large class of planning problems with nonlinear welfare functions, interacting treatments, learning, and noncooperative aspects.