6 ms·

An example of IRV's misbehaviour: * 8 people vote: A, C, B * 5 people vote: B, C, A * 4 people vote: C, B, A IRV eliminates C and elects B, but the majority

An example of IRV's misbehaviour: * 8 people vote: A, C, B * 5 people vote: B, C, A * 4 people vote: C, B, A IRV eliminates C and elects B, but the majority of voters prefer C over B (12 to 5). The order of elimination dropped 8 ballots' information that they prefer C over B. To put that generally, IRV ignores the secondary preferences of large demographics. Perhaps another example of why I think single winner voting systems should take all preferences into account (as Condorcet methods do): * 100 people vote CentristX * 101 people vote PolarizedCandidateA > CentristX * 101 people vote PolarizedCandidateB > CentristX * 101 people vote PolarizedCandidateC > CentristX * 101 people vote PolarizedCandidateD > CentristX The example is a bit contrived, but it highlights how disregarding secondary preferences (IRV's main feature) isn't a good idea. 403 people prefer CentristX over every other polarized candidate, yet CentristX is dropped in IRV's first round. Disclaimer: I run modernballots, a voting website that makes use of the Schulze-family of voting systems: https://modernballots.com/elections/zombies/vote/ https://modernballots.com/elections/zombies/vote/

mjhoy 10y ago
How often is this sort of thing actually a problem? Are there examples of elections that turned out this way?
- bradbeattie 10y ago
  The difficulty here is parsing out * people's sincere preferences * people's reported preferences in surveys * people's strategic voting in a hypothetical scenario * and people's strategic voting in the real world. I'd argue that an ideal system allows those four to collapse into one, but I'm not holding my breath. In honesty though, I don't know. I'd assume this type of failure would occur whenever the largest demographic's second choice isn't the first choice of the second largest demographic (read: quite often), but that's armchair guessing.
  - mjhoy 10y ago
    I read through the links in the comment above, and I'm not convinced by many of the arguments, including the theoretical voting situations, because it seems they are quite unrealistic in practice, while the current two-party system has many times given us a bad result that would have been solved by ranked choice. I'm thinking about actual Maine politics here. (Although I grant that this has the potential to change the existing liberal/conservative dynamics entirely.) I'm much more convinced about the argument against complexity, because I don't trust the state government much to design something clear and simple, and it's not yet clear to me that ranked choice is "simple". I hope they do. In any case I'm very excited to see what happens.
dragonwriter 10y ago
Without going through whole way to Condorcet methods, you can eliminate the problems associated with IRV's elimination step by just dropping the elimination step; set the election quota as the the smallest integer greater than half the ballots cast, if no one reaches the quota with just first preference votes, then add in second preference votes and see if there is a winner, and so on until someone wins. This also has (compared to both Condorcet methods and base IRV) relative simplicity of tallying ballots and processing them to get a result.
- naasking 10y ago
  Is this modification described or analyzed anywhere more thoroughly?
  - dragonwriter 10y ago
    With variations on whether (and at what ranks) you allow (and how you apply) equal rank votes, and how you resolve majorities that occur on the same round, it's corresponds roughly to the family of Bucklin [0] and Majority Choice Approval [1] methods. [0] http://wiki.electorama.com/wiki/Bucklin_voting http://wiki.electorama.com/wiki/Bucklin_voting [1] http://wiki.electorama.com/wiki/Majority_Choice_Approval http://wiki.electorama.com/wiki/Majority_Choice_Approval
    - naasking 10y ago
      Bucklin seems worse than IRV on every property except monotonicity: https://en.m.wikipedia.org/wiki/Single-member_district https://en.m.wikipedia.org/wiki/Single-member_district
      - dragonwriter 10y ago
        Well, it's actually identical on most criteria listed on that page (it's worse on Condorcet Loser and Clone Independence, which I'd argue are less important than Monotonicity, while still agreeing that Clone Independence is a real and practical concern; Condorcet Loser less so), but Bucklin's also not the best of the Bucklin/MCA family. Go back to the link I provided upthread and look at the analysis of the MCA variants (which Wikipedia doesn't include); most versions of MCA also satisfy Clone Independence. Bucklin and most MCA variants are also summable (mostly k=1, some k=2), while IRV is not summable [0]; this is an important trait for verifiable large elections which Wikipedia'so table omits. [0] http://wiki.electorama.com/wiki/Summability_criterion http://wiki.electorama.com/wiki/Summability_criterion

mjhoy 10y ago

How often is this sort of thing actually a problem? Are there examples of elections that turned out this way?

bradbeattie 10y ago
The difficulty here is parsing out * people's sincere preferences * people's reported preferences in surveys * people's strategic voting in a hypothetical scenario * and people's strategic voting in the real world. I'd argue that an ideal system allows those four to collapse into one, but I'm not holding my breath. In honesty though, I don't know. I'd assume this type of failure would occur whenever the largest demographic's second choice isn't the first choice of the second largest demographic (read: quite often), but that's armchair guessing.
- mjhoy 10y ago
  I read through the links in the comment above, and I'm not convinced by many of the arguments, including the theoretical voting situations, because it seems they are quite unrealistic in practice, while the current two-party system has many times given us a bad result that would have been solved by ranked choice. I'm thinking about actual Maine politics here. (Although I grant that this has the potential to change the existing liberal/conservative dynamics entirely.) I'm much more convinced about the argument against complexity, because I don't trust the state government much to design something clear and simple, and it's not yet clear to me that ranked choice is "simple". I hope they do. In any case I'm very excited to see what happens.

dragonwriter 10y ago

Without going through whole way to Condorcet methods, you can eliminate the problems associated with IRV's elimination step by just dropping the elimination step; set the election quota as the the smallest integer greater than half the ballots cast, if no one reaches the quota with just first preference votes, then add in second preference votes and see if there is a winner, and so on until someone wins. This also has (compared to both Condorcet methods and base IRV) relative simplicity of tallying ballots and processing them to get a result.

naasking 10y ago
Is this modification described or analyzed anywhere more thoroughly?
- dragonwriter 10y ago
  With variations on whether (and at what ranks) you allow (and how you apply) equal rank votes, and how you resolve majorities that occur on the same round, it's corresponds roughly to the family of Bucklin [0] and Majority Choice Approval [1] methods. [0] http://wiki.electorama.com/wiki/Bucklin_voting http://wiki.electorama.com/wiki/Bucklin_voting [1] http://wiki.electorama.com/wiki/Majority_Choice_Approval http://wiki.electorama.com/wiki/Majority_Choice_Approval
  - naasking 10y ago
    Bucklin seems worse than IRV on every property except monotonicity: https://en.m.wikipedia.org/wiki/Single-member_district https://en.m.wikipedia.org/wiki/Single-member_district
    - dragonwriter 10y ago
      Well, it's actually identical on most criteria listed on that page (it's worse on Condorcet Loser and Clone Independence, which I'd argue are less important than Monotonicity, while still agreeing that Clone Independence is a real and practical concern; Condorcet Loser less so), but Bucklin's also not the best of the Bucklin/MCA family. Go back to the link I provided upthread and look at the analysis of the MCA variants (which Wikipedia doesn't include); most versions of MCA also satisfy Clone Independence. Bucklin and most MCA variants are also summable (mostly k=1, some k=2), while IRV is not summable [0]; this is an important trait for verifiable large elections which Wikipedia'so table omits. [0] http://wiki.electorama.com/wiki/Summability_criterion http://wiki.electorama.com/wiki/Summability_criterion