An explanation of the continuing federal government mandate of single-member congressional districts

A formal rational expectation model is developed to explain why congressional single-member districts (SMD’s) were mandated in 1842 and why that mandate has repeatedly been re-affirmed. The tendency of voters to moderate the dominant party in the federal government combined with the single-party sweep effect of multi-member districts (MMD’s) creates the incentives for the strongest party to support a SMD mandate. This model performs empirically much better than alternative theories. The model’s prediction that the current SMD mandate is permanent is an example of how an institutional change can endure even if it no longer reflects voter preferences.