We recommended open-list proportional representation (OLPR) in the 2023 APSA report because we reasoned that MMP was not viable. MMP stands for “mixed-member PR,” a form of proportional representation that includes single-seat districts (SSD). Here is the rationale behind our recommendation, some potential objections to that advice, and a way to resuscitate something like MMP. I will call it minority-party representation (MPR).
MMP is a proportional system in the sense that a party’s share of seats matches its share of votes in a district as closely as possible. Often, that district is an entire country, but it does not have to be. Said district encapsulates several of one seat each. Proportionality comes from adding ‘at large’ seats to parties’ totals from the SSD contests. This is called compensation. The basis for compensation in a two-vote variant is the distribution of party votes, cast alongside voters’ choices in the SSD contests. In a one-vote variant, it is also the SSD vote.
There are two big constraints on using such a system for U.S. House elections. One is that compensation districts presumably cannot cross state lines. This flows from the constitutional requirement that seats be apportioned explicitly to states. As such, any MMP design aspiring to fine-grained proportionality would require a very large increase in overall chamber size so that compensation within states becomes practical. For this and other reasons, we recommended ‘simple’ list PR instead.
The second constraint is that MMP sometimes requires the number of seats in the compensation district to change. Let’s say two parties have gotten 65% and 35% of votes, respectively, in an eight-SSD state with some arbitrary number of additional, ‘at large’ compensation seats. The larger party wins seven seats (88%). How can the parties seat shares be brought closer to their vote shares? This might force us to resize the compensation district (AKA number of ‘at large’ seats). Similar processes in other states imply that the overall size of the House could vary from election to election, as might the number of seats in each state. While there is nothing wrong with this in principle, I can imagine it raising eyebrows and inviting conflict among state governments controlled by opposing parties. We come back to ‘simple’ list PR.
Yet MMP has fans. One group historically was the set of experts who believed that the absence of SSD caused party-system fragmentation in interwar Germany. More recently, MMP has been popular as a way to retain majority-minority and minority-influence SSD. Finally, there are politicians used to running in and representing SSD.
Here is an alternative called minority-party representation (MPR). I call it that because its main effect would be to give more seats to the largest underrepresented party in each state. Start with some modest addition to the overall size of the House.1 Apportion these seats to states in proportion to their populations. These seats then become ‘at large’ in any state that gets them. At each election, allocate these seats to parties in declining order of their deviations from seats/votes proportionally, accounting for their seat numbers at each stage of the process.
Thus described, MPR would reduce the effects of gerrymandering and ‘natural’ packing/cracking under the current SSD regime.