Rational Inattention via Ignorance Equivalence

We introduce the concept of the ignorance equivalent to effectively summarize the payoff possibilities in a finite Rational Inattention problem. The ignorance equivalent is a unique fictitious action that is weakly preferable to all existing learning strategies and yet generates no new profitable learning opportunities when added to the menu of choices. We fully characterize the relationship between the ignorance equivalent and the optimal learning strategies. Agents with heterogeneous priors self-select their own ignorance equivalent, which gives rise to an expected-utility analogue of the Rational Inattention problem. The approach provides new insights for menu expansion, the formation of consideration sets, the value of information, and belief elicitation. In a strategic game of contract choice, the ignorance equivalent emerges naturally in equilibrium.