Expert advice to a voting body.

I provide a theory of information transmission in collective choice settings. In the model, an expert has private information on the effect of a policy proposal and communicates to a set of voters prior to a vote over whether or not to implement the proposal. In contrast to previous game-theoretic models of political communication, the results apply to situations involving multiple voters, multidimensional policy spaces and a broad class of voting rules. The results highlight how experts can use information to manipulate collective choices in a way that reduces the ex ante expected utilities of all voters. Opportunities for expert manipulation are the result of collective choice instability: all voting rules that allow collective preference cycles also allow welfare-reducing manipulative persuasion by an expert. The results challenge prevailing theories of institutions in which procedures are designed to maximize information transmission.