[taoistextremist]

I don't think STV presents any function that would really prevent gerrymandering. The only thing it might do is allow entry of third parties, but even that's not guaranteed. But a party could still design districts that they'd always have a shot at the second round in every district while other parties don't.

What could potentially help is to have a legislative body not determined by geography, possibly some kind of proportional party system (the downside being you need to make parties a formal part of the system, but they'll always be present anyways), that must ratify redistricting proposals and can challenge currently drawn districts.

[dragonwriter]

> I don't think STV presents any function that would really prevent gerrymandering.

STV with multimember districts (not the degenerate single-member district form also known as IRV) limits the degree of distortion that you can get through how district lines are drawn (whether intentional gerrymandering or otherwise.)

[lambertsimnel]

"STV" actually refers to at least two related systems. You seem to be commenting on the single-winner form (also called "Instant Runoff Voting" in the United States). The multi-winner form is a form of proportional representation and as such would provide substantial protection from gerrymandering. The Australian terms "majority-preferential" and "quota-preferential" help make the difference (and the connection) clear.

[squiggleblaz]

I think the concern is that you could still, in principle, draw districts that gave you lots of seats, because they're relatively small. STV isn't proportional by design. You want as many of their votes as possible to wind up in the fourth of three quotas, and as many of yours as possible to end up in the three quotas that win seats. For instance, it may be that Us in some state just suddenly start winning two out of three seats in most districts. Make sure the two seat districts go in areas where They have a bit more than fifty percent but not a full two quotas so they split one apiece. The goal is still to waste as many of Their votes as possible to get fifty percent plus one seats.

PR is no panacea. To avoid gerrymandering, you need an adequately high district magnitude. After all, majority-preferential is just quota-preferential with a magnitude of 1. And FPTP is just List PR with a magnitude of 1.

[lambertsimnel]

You make many important points, but I don't agree that "STV isn't proportional by design". STV-PR provides voters with representatives elected by equal numbers of votes, and that's pretty close to the definition of proportionality. Given enough seats per constituency, STV-PR provides proportionality not only by party, but by any factors voters choose.

Anyway, I was responding to this:

>>> I don't think STV presents any function that would really prevent gerrymandering.

I still believe that STV-PR resists gerrymandering as much as List PR does.

> PR is no panacea. To avoid gerrymandering, you need an adequately high district magnitude.

I agree, but I expect any form of PR would deal a substantial blow to gerrymandering, even if it isn't a panacea. Perhaps the only way to eliminate gerrymandering is to elect all representatives from a single multi-member constituency. (I expect any other system with enough compensatory List PR seats would be practically as resistant to gerrymandering.) Of course, the sticking point for STV-PR is that a ballot paper for STV435 wouldn't be very user friendly :) .

What do you think of STV+ as a compromise? Under STV+ most representatives are elected under STV-PR and a minority are elected through compensatory List PR to increase the precision of party proportionality.

[taoistextremist]

STV itself merely refers to the voting system. If by "multi-winner" you mean multimember districts, that's still very susceptible to gerrymandering. Anything involving districting is, you can still split up populations so they have weaker representation, even under proportional systems, by making their representation much weaker in many districts and overly strong in a few.

I think Germany has a good solution where there's single-winner districts along with a proportional list. I also think giving authority of redistricting to an authority that can't directly benefit from it could also work.

[lambertsimnel]

> If by "multi-winner" you mean multimember districts

That is what I mean. (In theory you could have an election with one enormous constituency under STV, but I accept that it wouldn't be very practical at government level, even if it works well for electing the boards of non-profit organisations.)

> Anything involving districting is, you can still split up populations so they have weaker representation, even under proportional systems, by making their representation much weaker in many districts and overly strong in a few.

True, but if I understand correctly that's about unequal district population, rather than gerrymandering. Proportional systems with a single constituency or compensatory List PR largely avoid concerns about districting.

> I think Germany has a good solution where there's single-winner districts along with a proportional list.

Germany does indeed have a good system, but I'd prefer it without the single-winner districts and with most representatives elected by STV (ie, the STV+ system described in the last paragraph of my other post: https://news.ycombinator.com/item?id=15970289 ).

[dragonwriter]

> If by "multi-winner" you mean multimember districts, that's still very susceptible to gerrymandering.

No, it's not. With any proportional system (including STV), the more members per district, the less distortion is theoretically possible through differences in how district lines are drawn.