Competitive equilibrium in markets for votes

We develop a competitive equilibrium theory of a market for votes. Before voting on a binary issue, individuals may buy and sell their votes with each other. We define the concept of ex ante vote-trading equilibrium, and show by construction that an equilibrium exists. The equilibriumwe characterize always results in dictatorship if there is any trade, and the market for votes generates welfare losses, relative to simple majority voting, if the committee is large enough or the distribution of values not very skewed. We test the theoretical implications by implementing a competitive vote market in the laboratory using a continuous open-book multi-unit double auction.