In Defense of Exclusionary Deliberation: Communciation and Voting with Private Beliefs and Values

Fundamentally, deliberative democracy is an institution in which participants communicate and then vote. We analyze strategic behavior in this type of institution when agents do not necessarily have common beliefs and values. The potential for some pairs of participants to have diametrically opposed preferences makes it difficult to support equilibria in which participants truthfully reveal their private information. Nonetheless, truthful equilibria are shown to exits for some (but not all) parameterizations in which non-common values are likely. Truthful equilibria exist if and only if participants of all possible preference types believe that it is likely that a majority of the others share their preference type. Even when truthful equilibria fail to exist, the probability that the collective choice corresponds to that which a majority would choose, with full-information, approaches one as population size tends to infinity. Despite this limiting efficiency, larger groups need not outperform smaller groups as truthful equilibria are easier to support with small deliberative bodies. The design of deliberative institutions to aggregate information involves a trade-off between the statistical benefit of more participants and the strategic problems associated with information transmission in larger settings without common values. For many reasonable parameterizations, the latter effect is dominant and excluding randomly chosen participants is desirable.