Expert information and majority decisions

This paper shows theoretically and experimentally that hearing expert opinions can be a double-edged sword for collective decision making. We present a majoritarian voting game of common interest where committee members receive not only private information, but also expert information that is more accurate than private information and observed by all members. In theory, there are Bayesian Nash equilibria where the committee members’ voting strategy incorporates both types of information and access to expert information enhances the efficiency of the majority decision. However, there is also a class of potentially inefficient equilibria where a supermajority always follow expert information and the majority decision does not aggregate private information. In the laboratory, the majority decisions and the subjects’ voting behaviour were largely consistent with those in the class of inefficient equilibria. We found a large efficiency loss due to the presence of expert information especially when the committee size was large. We suggest that it may be desirable for expert information to be revealed only to a subset of committee members.