Voting Systems

Jean-Rémi Desjardins - Scala Days Chicago 2017

First Past the Post

  • US, Canada, UK, India, ...
  • 2nd most popular system (British Empire)
  • Form of plural voting (most votes wins)
  • Ideal for scenarios with two choices
  • Terrible for sceanrios with more choices
    • "strategic voting"
    • "wasted votes"
  • Very simple to understand
  • Very simple to cast vote

Ranked Voting

  • Australia, Hong Kong, Ireland, New Zealand
  • Form of majoritarian voting (must have a majority)
  • Deals well with scenarios with more than two options
  • Variants on how to cast and how to tally the vote (IRV, Borda)
  • IRV and STV are only variants in use in goverment
  • Arrow's impossibility theorem
  • Can elect a Condorcet winner
  • Simple enough to understand
  • Very simple to cast vote

Arrow's IMpossibility theorem

  • if every voter prefers alternative X over alternative Y, then the group prefers X over Y
  • If every voter's preference between X and Y remains unchanged, then the group's preference between X and Y will also remain unchanged (even if voters' preferences between other pairs like X and Z, Y and Z, or Z and W change).
  • There is no "dictator": no single voter possesses the power to always determine the group's preference.

Range Voting

  • Amazon, Yelp, ...
  • Deals very well with scenarios with more than two options
  • How to deal with "little known" candidates
  • Simple to understand except for above bullet
  • Simple enough to cast vote

Approval Voting

  • American Mathematical Society
  • Form of plurality voting (most votes win)
  • Special case of Range Voting
  • Deals pretty well with scenarios with more than two options
  • Very simple to understand
  • Casting the vote is even simpler than "first past the post"

Two-round system

  • France, Brazil, India, many more
  • Most popular presidential election system
  • Form of majoratarian voting (must have a majority)
  • Better than "First Past The Post"...
  • Very similar to some variants of Ranked Voting
  • Candidates can "shift" their positions after the first round
  • Simple to understand
  • Simple enough to cast vote

Proportional Representation

  • Most widely used system for legislatures
  • Suitable for non "single seat" scenarios
  • Can be difficult to understand re-distribution rules
  • Largely orthogonal to previous systems

Final Notes

  • Is geographic location really the best way to separate constituencies?
  • Would profession, age, income be better in the 21st century?
  • What about variable sized constituencies?
  • What if citizens could vote on any issue?

Voting Systems

By Jean-Rémi Desjardins

Voting Systems

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