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← Which voting system is the best? - Alex Gendler

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Mostrar Revisión1 creada 06/10/2020 por lauren mcalpine .

  1. Imagine we want to build a new space port
  2. at one of four recently settled
    Martian bases,
  3. and are holding a vote
    to determine its location.
  4. Of the hundred colonists on Mars,
    42 live on West Base, 26 on North Base,
  5. 15 on South Base, and 17 on East Base.
  6. For our purposes, let’s assume
    that everyone prefers the space port
  7. to be as close to their base as possible,
    and will vote accordingly.
  8. What is the fairest way
    to conduct that vote?
  9. The most straightforward solution
    would be to just let each individual

  10. cast a single ballot, and choose
    the location with the most votes.
  11. This is known as plurality voting,
    or "first past the post."
  12. In this case, West Base wins easily,
  13. since it has more residents
    than any other.
  14. And yet, most colonists would consider
    this the worst result,
  15. given how far it is from everyone else.
  16. So is plurality vote
    really the fairest method?
  17. What if we tried a system
    like instant runoff voting,

  18. which accounts for the full range
    of people’s preferences
  19. rather than just their top choices?
  20. Here’s how it would work.
  21. First, voters rank
    each of the options from 1 to 4,
  22. and we compare their top picks.
  23. South receives the fewest votes
    for first place, so it’s eliminated.
  24. Its 15 votes get allocated
    to those voters’ second choice—
  25. East Base— giving it a total of 32.
  26. We then compare top preferences
    and cut the last place option again.
  27. This time North Base is eliminated.
  28. Its residents’ second choice
    would’ve been South Base,
  29. but since that’s already gone,
    the votes go to their third choice.
  30. That gives East 58 votes over West’s 42,
    making it the winner.
  31. But this doesn’t seem fair either.
  32. Not only did East start out
    in second-to-last place,
  33. but a majority ranked it among
    their two least preferred options.
  34. Instead of using rankings, we could try
    voting in multiple rounds,

  35. with the top two winners
    proceeding to a separate runoff.
  36. Normally, this would mean West and North
    winning the first round,
  37. and North winning the second.
  38. But the residents of East Base realize
  39. that while they don’t have
    the votes to win,
  40. they can still skew the results
    in their favor.
  41. In the first round, they vote
    for South Base instead of their own,
  42. successfully keeping North
    from advancing.
  43. Thanks to this "tactical voting"
    by East Base residents,
  44. South wins the second round easily,
    despite being the least populated.
  45. Can a system be called fair and good
    if it incentivizes lying
  46. about your preferences?
  47. Maybe what we need to do
    is let voters express a preference

  48. in every possible head-to-head matchup.
  49. This is known as the Condorcet method.
  50. Consider one matchup:
    West versus North.
  51. All 100 colonists vote on their preference
    between the two.
  52. So that's West's 42 versus
    the 58 from North, South, and East,
  53. who would all prefer North.
  54. Now do the same
    for the other five matchups.
  55. The victor will be whichever base
    wins the most times.
  56. Here, North wins three
    and South wins two.
  57. These are indeed the two
    most central locations,
  58. and North has the advantage of not being
    anyone’s least preferred choice.
  59. So does that make the Condorcet method
    an ideal voting system in general?

  60. Not necessarily.
  61. Consider an election
    with three candidates.
  62. If voters prefer A over B, and B over C,
    but prefer C over A,
  63. this method fails to select a winner.
  64. Over the decades, researchers
    and statisticians have come up with

  65. dozens of intricate ways
    of conducting and counting votes,
  66. and some have even been
    put into practice.
  67. But whichever one you choose,
  68. it's possible to imagine it delivering
    an unfair result.
  69. It turns out that our intuitive concept
    of fairness

  70. actually contains a number of assumptions
    that may contradict each other.
  71. It doesn’t seem fair for some voters
    to have more influence than others.
  72. But nor does it seem fair to simply
    ignore minority preferences,
  73. or encourage people to game the system.
  74. In fact, mathematical proofs
    have shown that for any election
  75. with more than two options,
  76. it’s impossible to design a voting system
    that doesn’t violate
  77. at least some theoretically
    desirable criteria.
  78. So while we often think of democracy
    as a simple matter of counting votes,
  79. it’s also worth considering who benefits
    from the different ways of counting them.