Evaluating Information in Zero-Sum Games with Incomplete Information on Both Sides

We study zero-sum games with incomplete information and analyze the impact that the information players receive has on the payoffs. It turns out that the functions that measure the value of information share two properties. The first is Blackwell monotonicity, which means that each player gains from knowing more. The second is concavity on the space of conditional probabilities. We prove that any function satisfying these two properties is the value function of a zero-sum game.