Comparison of information structures

Several authors have observed that in interactive decision frameworks, welfare is not monotonic with information in the sense that more information can make agents worse off. This contrasts with Blackwell’s comparison of statistical experiments in which more information can only make the statistician better off. We introduce the notion of an information structure L as being richer than another J when for every game G, all correlated equilibrium distributions of G induced by J are also induced by L. If L is richer than J, L can always make all agents as well off than J. We also define J to be faithfully reproducible from L when all the players can compute from their information in L “new information” that reproduces what they could have received from J . Our main result is that L is richer than J if and only if J is faithfully reproducible from L.