Mixed Motives and the Optimal Size of Voting Bodies

We study a Condorcet jury model where voters are driven by instrumental and expressive motives. We show that arbitrarily small amounts of expressive motives significantly affect equilibrium behavior and the optimal size of voting bodies. Enlarging voting bodies always reduces accuracy over some region. Unless conflict between expressive and instrumental preferences is very low, information does not aggregate in the limit, and large voting bodies perform no better than a coin flip in selecting the correct outcome. Thus, even when adding informed voters is costless, smaller voting bodies often produce better decisions.