Is the single transferable vote a form of proportional representation? Right now I believe it is. A reviewer once said the fight had been won. Either way, this issue stops some of my talks dead in their tracks. Some are bothered that PR might coexist with candidate-based ballots.
Yet among the countries (and subnational units) we usually think of as having PR, early adopters often went for candidate-based ballots (e.g., Switzerland). A working hypothesis is that STV is just one of several PR systems whose debut predates the mass party. PR systems like these find appeal where politicians, for whatever reason, want some level of distinction from their party’s brand.
This page exists to collect my evolving thoughts on the issue. I plan to update it as needed.
Regardless of whether STV is “PR,” one thing is certain: it definitely is not a plurality or majority voting rule. If a party is a team that seeks control of government, it needs to be very popular to win that under STV.
The case against STV as PR
Matthew Shugart says STV can operate more like the single non-transferable vote, which, all else equal, gives politicians little reason to be good “party men” (Carey and Shugart 1995). I don’t think he would say STV is strictly not PR.
Farrell and Katz (2014) say STV was “invented” before mass parties emerged. That doesn’t mean it’s not PR. Nor does it mean it is. It depends on what we mean by “PR.”
The case for STV as PR
Bormann and Golder (2013) classify STV as a PR system because it relies on a quota for seat allocation.
Charles Buckalew (1872) reviews the PR literature up to 1872. There is scant evidence of PR being party-based. Buckalew promoted a system called cumulative voting, used for Illinois state legislative elections until 1980, and which today exists in some cities with racism problems.
John Commons (1896) distinguishes between the Hare (i.e., STV) and Gove systems, neither of which is party-based.
Edmund James (1896) refers to the operation of the “free list” system in Switzerland. This is an open-list PR rule. But note: Swiss voters are not restricted to choice within one party’s list. There are many ways in which they can disturb more than one party list. This is called panachage. Los Angeles voters rejected something like this in a 1913 referendum (Sitton 1995). The idea of choice among candidates across party lists strongly resembles STV.