Document Type
Dataset
DOI
https://doi.org/10.21974/xw1s-yj16
Publication Date
2026
Abstract
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.
Description
Replication data and code for "Mixed-Member Proportional Representation and the U.S. House of Representatives" published in Political Research Quarterly by Alex Keena, Oscar Pocasangre, and Natasha Romero Moskala at: https://doi.org/10.1177/10659129261444345
File descriptions:
Data files
1) House 2024.csv - candidate level election results for the 2024 House elections
2) Presidential_2024.csv - presidential candidate level election results for the 2024 election
3) state_pop.csv - state level population (2020)
4) state_party_votes.csv - pooled party votes at the state level, from House election data
5) house_district_seat_shares.csv - for parties that won seats, the number of seats they won in each state, total number of seats to be won in the state, and the share of seats each party won at the state level.
R Scripts
1) MMP Seat Allocation Procedures - carries out the allocation of seats using the MMP methods for a House size of 870.
2) MMM Seat Allocation Procedures - carries out allocation of seats using MMM methods for a House size of 870.
3) MMP Disproportionality Index Calculations - includes function that calculates the average Gallagher Index across states for varying House sizes using MMP procedures.
4) MMM Disproportionality Index Calculations - includes function that calculates the average Gallagher Index across states for varying House sizes using MMM procedures.
File Format
.tiff, .csv, .txt, .R
Language
English
Is Part Of
VCU Political Science Data
Date of Submission
4-28-2026