Post by @timbray@cosocial.ca

Was hearing about the #newzealand election (results: inconclusive) and realized that I totally didn’t understand the difference between “MMP” and “MMR” proportional representation. I’m abstractly a big fan of PR and wish we had it in Canada but hadn’t appreciated the complex taxonomy of flavors of PR.

- MMP https://en.wikipedia.org/wiki/Mixed-member_proportional_representation
- MMR https://en.wikipedia.org/wiki/Mixed-member_majoritarian_representation

Then there’s Ranked-Choice, on which I’m dubious because the algorithm is non-obvious [UPDATE: Meant to say “has weird corner cases]

Mixed-member majoritarian representation

type of mixed electoral system

Mixed-member proportional representation

mixed electoral system centered on proportional representation with single-member district elements

#newzealand

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Colin Jackson

@ThisCJ@mastodon.nz 3 hr. ago

@timbray I once researched that algorithm and wrote it up: https://internetnz.nz/governance-and-reports/our-board/board-elections/internetnz-electoral-system-explanation/

InternetNZ electoral system (explanation)

Learn how the Council elections are carried out at InternetNZ. We've detailed the process and conduct followed for each round.

Tim Bray 🇨🇦

@timbray@cosocial.ca 3 hr. ago

@ThisCJ It can get weird and complex though, see https://en.wikipedia.org/wiki/Arrow%27s_impossibility_theorem

Arrow's impossibility theorem

Result that no ranked-choice system is spoilerproof

Larry Garfield

@Crell@phpc.social 3 hr. ago

@timbray @ThisCJ Every voting system has a failure mode. In practice, RCV rarely hits its failure mode. (twice in over 600 RCV elections in the US this century.)

Also in practice, voters find RCV easy to understand and use and are happier with the result.

Proportional only works for a large constituency electing by party, not person. I'd rather elect people than parties. Proportional RCV handles multi-member districts just fine.

M. Grégoire

@mpjgregoire@cosocial.ca 2 hr. ago

@ThisCJ I'm interested in RCV. Could you please share a reference for your first claim?

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Tim Bray 🇨🇦

@timbray@cosocial.ca 3 hr. ago

@Crell @ThisCJ Fair enough, but there’s this bug in FPTPP that I think only MMR/MMM can really address? It takes the form of “Party got X% of the popular vote but only won Y% of the seats in parliament”, where Y is dramatically less than X.

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