Mixed-Member Proportional Representation and the U.S. House of Representatives

The use of single-seat districts and majoritarian rules for legislative elections is associated with many problems in American politics. However, this method of electing legislators to the U.S. House of Representatives can be reformed through acts of Congress. We investigate the potential of mixed-member electoral systems, which have gained popularity among reformers for potentially providing the “best of both worlds.” We review the comparative scholarship to clarify the mechanics of mixed-member systems, particularly how mixed-member proportional systems (MMP) balance the representational goals of dyadic, localized representation with proportional party representation. We model an MMP system for the House to see whether it can address problems such as the two-party system and gerrymandering. Using data from the 2024 House elections and the 2025 mid-decade redistricting, we find that an MMP system that significantly expands the size of the House would improve the alignment of votes to seats at the state level, increase third party seats, and neutralize partisan bias in gerrymandering. Our analysis demonstrates that specific design choices (assembly size, seat linkage, and apportionment formulas) shape the system’s effectiveness. Our exercise underscores the potential benefits and challenges of MMP as a reform option for the U.S.