Consensus and the Accuracy of Signals: Optimal Committee Design with Information Acquisition

We present a model of private production of information in collective decision making. Agents gather costly information, and then aggregate it to produce a collective decision. Because information is a public good, it will be underprovided relative to the social optimum. A ``good'' mechanism must then give incentives to acquire information, as well as aggregate information efficiently. We characterize the voting mechanism that produces the most informed decision. We obtain a necessary condition for the optimal voting rule to be ``consensual'', i.e. close to unanimity or veto power: a consensual voting rule can be optimal only if the information available to each agent is sufficiently accurate. This condition is independent of the preferences of voters and of the cost of information, and links the voting rule to the quality of information available to agents. Our results are robust to introducing heterogeneity of agents.