SLIDE 1 The Mathematics of Elections Kim Klinger-Logan
February 2019 It’s not the voting that’s democracy; it’s the counting. – Tom Stoppard, Jumpers
SLIDE 2
In the news . . .
Bangor Daily News
SLIDE 3
Ranked Choice Voting
Consider the following preference ballot in a Math Club Election. 1st: Carmen 2nd: Ben 3rd: Darius 4th: Alice
SLIDE 4
Ranked Choice Voting
Consider the following preference ballot in a Math Club Election. 1st: Carmen 2nd: Ben 3rd: Darius 4th: Alice What does this ballot tell us about the voter’s preferences?
SLIDE 5
Ranked Choice Voting
Consider the following preference ballot in a Math Club Election. 1st: Carmen 2nd: Ben 3rd: Darius 4th: Alice What does this ballot tell us about the voter’s preferences? Well it obviously tells us the order of the voter’s preferences. It also tells us unequivocally which candidate the voter would choose between any two candidates (i.e. between A and B the voter would choose B). Finally, the relative preferences of the ballot would not change if one of the candidates withdraws or is eliminated.
SLIDE 6
Ranked Choice Voting
Suppose we have the following small batch of ballots 1st: C 2nd: D 3rd: B 4th: A 1st: D 2nd: C 3rd: B 4th: A 1st: C 2nd: B 3rd: D 4th: A 1st: A 2nd: B 3rd: C 4th: D 1st: C 2nd: B 3rd: D 4th: A 1st: A 2nd: B 3rd: C 4th: D 1st: D 2nd: C 3rd: B 4th: A 1st: A 2nd: B 3rd: C 4th: D 1st: B 2nd: D 3rd: C 4th: A 1st: A 2nd: B 3rd: C 4th: D A: Alice, B: Ben, C: Carmen, and D: Darius How do we count these ballots? Number of Voters: 1st: A C D B C 2nd: B B C D D 3rd: C D B C B 4th: D A A A A
SLIDE 7
Ranked Choice Voting
Suppose we have the following small batch of ballots 1st: C 2nd: D 3rd: B 4th: A 1st: D 2nd: C 3rd: B 4th: A 1st: C 2nd: B 3rd: D 4th: A 1st: A 2nd: B 3rd: C 4th: D 1st: C 2nd: B 3rd: D 4th: A 1st: A 2nd: B 3rd: C 4th: D 1st: D 2nd: C 3rd: B 4th: A 1st: A 2nd: B 3rd: C 4th: D 1st: B 2nd: D 3rd: C 4th: A 1st: A 2nd: B 3rd: C 4th: D A: Alice, B: Ben, C: Carmen, and D: Darius How do we count these ballots? Number of Voters: 4 2 2 1 1 1st: A C D B C 2nd: B B C D D 3rd: C D B C B 4th: D A A A A
SLIDE 8
Math Club Election
Suppose we count the rest of the ballots and we end up with the following preference schedule: Number of Voters: 14 10 8 4 1 1st: A C D B C 2nd: B B C D D 3rd: C D B C B 4th: D A A A A A: Alice, B: Ben, C: Carmen, and D: Darius
SLIDE 9
Math Club Election
Suppose we count the rest of the ballots and we end up with the following preference schedule: Number of Voters: 14 10 8 4 1 1st: A C D B C 2nd: B B C D D 3rd: C D B C B 4th: D A A A A A: Alice, B: Ben, C: Carmen, and D: Darius Who is the winner of the election?
SLIDE 10
The candidate with the most first place votes is winner, the candidate with the second most votes is second, and so on.
SLIDE 11
The candidate with the most first place votes is winner, the candidate with the second most votes is second, and so on. What happens in the Math Club Election using the Plurality Method?
SLIDE 12
The candidate with the most first place votes is winner, the candidate with the second most votes is second, and so on. What happens in the Math Club Election using the Plurality Method? Number of Voters: 14 10 8 4 1 1st: A C D B C 2nd: B B C D D 3rd: C D B C B 4th: D A A A A
SLIDE 13
The candidate with the most first place votes is winner, the candidate with the second most votes is second, and so on. What happens in the Math Club Election using the Plurality Method? Number of Voters: 14 10 8 4 1 1st: A C D B C 2nd: B B C D D 3rd: C D B C B 4th: D A A A A Alice is 1st, Carmen is 2nd, Darius is 3rd and Ben is 4th.
SLIDE 14
Plurality Method
What is the appeal of this method?
SLIDE 15
Plurality Method
What is the appeal of this method? simplicity
SLIDE 16
Plurality Method
What is the appeal of this method? simplicity What are the potential problems with this method?
SLIDE 17 Plurality Method
What is the appeal of this method? simplicity What are the potential problems with this method?
- 1. When there are more than two candidates we can end up with
a winner that does not have more than 50% of the votes.
SLIDE 18 Plurality Method
What is the appeal of this method? simplicity What are the potential problems with this method?
- 1. When there are more than two candidates we can end up with
a winner that does not have more than 50% of the votes.
- 2. The closeness of the election: This causes it to be the most
easily manipulated by insincere voters.
SLIDE 19 Plurality Method
What is the appeal of this method? simplicity What are the potential problems with this method?
- 1. When there are more than two candidates we can end up with
a winner that does not have more than 50% of the votes.
- 2. The closeness of the election: This causes it to be the most
easily manipulated by insincere voters.
- 3. A candidate may be preferred by voters over all other
candidates yet not win.
SLIDE 20 Plurality Method
What is the appeal of this method? simplicity What are the potential problems with this method?
- 1. When there are more than two candidates we can end up with
a winner that does not have more than 50% of the votes.
- 2. The closeness of the election: This causes it to be the most
easily manipulated by insincere voters.
- 3. A candidate may be preferred by voters over all other
candidates yet not win.
Number of Voters: 14 10 8 4 1 1st: A C D B C 2nd: B B C D D 3rd: C D B C B 4th: D A A A A
SLIDE 21
In an election with n candidates, we give 1 point for last place, 2 points for second from the last place and so on so that the first place candidate gets n points.
SLIDE 22
In an election with n candidates, we give 1 point for last place, 2 points for second from the last place and so on so that the first place candidate gets n points.The candidate with the most points wins the candidate with the second most points gets second place, and so on.
SLIDE 23
In an election with n candidates, we give 1 point for last place, 2 points for second from the last place and so on so that the first place candidate gets n points.The candidate with the most points wins the candidate with the second most points gets second place, and so on. What happens in the Math Club Election using the Borda Count Method?
SLIDE 24
In an election with n candidates, we give 1 point for last place, 2 points for second from the last place and so on so that the first place candidate gets n points.The candidate with the most points wins the candidate with the second most points gets second place, and so on. What happens in the Math Club Election using the Borda Count Method? Number of Voters: 14 10 8 4 1 1st (4pts): A C D B C 2nd (3pts): B B C D D 3rd (2pts): C D B C B 4th (1pts): D A A A A
SLIDE 25
In an election with n candidates, we give 1 point for last place, 2 points for second from the last place and so on so that the first place candidate gets n points. The candidate with the most points wins the candidate with the second most points gets second place, and so on. What happens in the Math Club Election using the Borda Count Method? Number of Voters: 14 10 8 4 1 1st (4pts): A (56) C D B C 2nd (3pts): B B C D D 3rd (2pts): C D B C B 4th (1pts): D A (10) A (8) A (4) A (1) A: 56+10+8+4+1 = 79 pts
SLIDE 26
In an election with n candidates, we give 1 point for last place, 2 points for second from the last place and so on so that the first place candidate gets n points. The candidate with the most points wins the candidate with the second most points gets second place, and so on. What happens in the Math Club Election using the Borda Count Method? Number of Voters: 14 10 8 4 1 1st (4pts): A (56) C (40) D (32) B (16) C (4) 2nd (3pts): B (42) B (30) C (24) D (12) D (3) 3rd (2pts): C (28) D (20) B (16) C (8) B (2) 4th (1pts): D (14) A (10) A (8) A (4) A (1) A: 56+10+8+4+1 = 79 pts B: 42+30+16+16+2 = 106 pts Ben wins (then C: 28+40+24+8+4 = 104 pts Carmen, Darius D: 14+20+32+12+3 = 81 pts and Alice).
SLIDE 27
- III. Plurality-with-Elimination Method
◮ Round 1: Count the 1st place votes for each candidate, just
as you would in the plurality method. If a candidate has a majority of 1st place votes, then that candidate is the winner. Otherwise, eliminate the candidate(s) with the fewest 1st place votes.
◮ Round 2: Cross out the names of the candidates eliminated
from the preference schedule and transfer those votes to the next eligible candidates on those ballots. Recount the votes. If a candidate has a majority then declare that candidate the
- winner. Otherwise eliminate the candidate with the fewest
votes.
◮ Round 3, 4, . . . : Repeat the process, each time eliminating
the candidate with the fewest votes and transferring those votes to the next eligible candidate. Continue until there is a candidate with the majority. That candidate is the winner of the election.
SLIDE 28
Plurality-with-Elimination Method
What happens in the Math Club Election using the Plurality-with-Elimination Method?
SLIDE 29
Plurality-with-Elimination Method
What happens in the Math Club Election using the Plurality-with-Elimination Method? Number of Voters: 14 10 8 4 1 1st: A C D B C 2nd: B B C D D 3rd: C D B C B 4th: D A A A A
SLIDE 30 Plurality-with-Elimination Method
What happens in the Math Club Election using the Plurality-with-Elimination Method? Number of Voters: 14 10 8 4 1 1st: A C D B C 2nd: B B C D D 3rd: C D B C B 4th: D A A A A Round 1: First place votes for . . . A=14, B =4, C=11, and D=8
SLIDE 31 Plurality-with-Elimination Method
What happens in the Math Club Election using the Plurality-with-Elimination Method? Number of Voters: 14 10 8 4 1 1st: A C D B C 2nd: B B C D D 3rd: C D B C B 4th: D A A A A Round 1: First place votes for . . . A=14, B =4, C=11, and D=8
- ut of 37 votes. No winner so eliminate B.
SLIDE 32 Plurality-with-Elimination Method
What happens in the Math Club Election using the Plurality-with-Elimination Method? Number of Voters: 14 10 8 4 1 1st: A C D B C 2nd: B B C D D 3rd: C D B C B 4th: D A A A A Round 1: First place votes for . . . A=14, B =4, C=11, and D=8
- ut of 37 votes. No winner so eliminate B.
Round 2: B’s votes go to D. First place votes for . . . A=14, C=11, and D=12.
SLIDE 33 Plurality-with-Elimination Method
What happens in the Math Club Election using the Plurality-with-Elimination Method? Number of Voters: 14 10 8 4 1 1st: A C D B C 2nd: B B C D D 3rd: C D B C B 4th: D A A A A Round 1: First place votes for . . . A=14, B =4, C=11, and D=8
- ut of 37 votes. No winner so eliminate B.
Round 2: B’s votes go to D. First place votes for . . . A=14, C=11, and D=12. No winner so eliminate C.
SLIDE 34 Plurality-with-Elimination Method
What happens in the Math Club Election using the Plurality-with-Elimination Method? Number of Voters: 14 10 8 4 1 1st: A C D B C 2nd: B B C D D 3rd: C D B C B 4th: D A A A A Round 1: First place votes for . . . A=14, B =4, C=11, and D=8
- ut of 37 votes. No winner so eliminate B.
Round 2: B’s votes go to D. First place votes for . . . A=14, C=11, and D=12. No winner so eliminate C. Round 3: C’s votes go to D. First place votes for . . . A=14 and D=23. D is the winner (then A, C and B).
SLIDE 35 Plurality-with-Elimination Method
What happens in the Math Club Election using the Plurality-with-Elimination Method? Number of Voters: 14 10 8 4 1 1st: A C D B C 2nd: B B C D D 3rd: C D B C B 4th: D A A A A Round 1: First place votes for . . . A=14, B =4, C=11, and D=8
- ut of 37 votes. No winner so eliminate B.
Round 2: B’s votes go to D. First place votes for . . . A=14, C=11, and D=12. No winner so eliminate C. Round 3: C’s votes go to D. First place votes for . . . A=14 and D=23. D is the winner (then A, C and B). Trump v. Clinton 2016
SLIDE 36
- IV. Method Pairwise Comparisons
Given any two candidates, we can count how many voters votes
- ne above the other and vice versa, the one with the highest
number wins the pairwise comparison. For each possible pairwise comparison between candidates, give 1 point to the winner and 0 points to the loser (if a tie, give each 1/2 a point). The candidate with the most points is the winner.
SLIDE 37
- IV. Method Pairwise Comparisons
Given any two candidates, we can count how many voters votes
- ne above the other and vice versa, the one with the highest
number wins the pairwise comparison. For each possible pairwise comparison between candidates, give 1 point to the winner and 0 points to the loser (if a tie, give each 1/2 a point). The candidate with the most points is the winner. What happens in the Math Club Election using the Method of Pairwise Comparisons?
SLIDE 38
- IV. Method Pairwise Comparisons
Given any two candidates, we can count how many voters votes
- ne above the other and vice versa, the one with the highest
number wins the pairwise comparison. For each possible pairwise comparison between candidates, give 1 point to the winner and 0 points to the loser (if a tie, give each 1/2 a point). The candidate with the most points is the winner. What happens in the Math Club Election using the Method of Pairwise Comparisons? Number of Voters: 14 10 8 4 1 1st: A C D B C 2nd: B B C D D 3rd: C D B C B 4th: D A A A A
SLIDE 39
- IV. Method Pairwise Comparisons
Given any two candidates, we can count how many voters votes
- ne above the other and vice versa, the one with the highest
number wins the pairwise comparison. For each possible pairwise comparison between candidates, give 1 point to the winner and 0 points to the loser (if a tie, give each 1/2 a point). The candidate with the most points is the winner. What happens in the Math Club Election using the Method of Pairwise Comparisons? Number of Voters: 14 10 8 4 1 1st: A C D B C 2nd: B B C D D 3rd: C D B C B 4th: D A A A A Pairwise Comparison: Votes: Winner: A OR B A (14); B (23) B
SLIDE 40
- IV. Method of Pairwise Comparisons
Given any two candidates, we can count how many voters votes
- ne above the other and vice versa, the one with the highest
number wins the pairwise comparison. For each possible pairwise comparison between candidates, give 1 point to the winner and 0 points to the loser (if a tie, give each 1/2 a point). The candidate with the most points is the winner. What happens in the Math Club Election using the Method of Pairwise Comparisons? Pairwise Comparison: Votes: Winner: A OR B A (14); B (23) B A OR C A (14); C (23) C A OR D A (14); D (23) D B OR C B (18); C (19) C B OR D B (28); D (9) B C OR D C (25); D (12) C C=3, B=2, D=1, A=0. Thus C is the winner!
SLIDE 41 Summary of Results
For the Math Club Election we had the following outcomes
- I. Plurality Method: A, C, D, B
- II. Borda Count Method: B, C, D, A
- III. Plurality-with-Elimination Method: D, A, C, B
- IV. Method of Pairwise Comparisons: C, B, D, A
SLIDE 42 Summary of Results
For the Math Club Election we had the following outcomes
- I. Plurality Method: A, C, D, B
- II. Borda Count Method: B, C, D, A
- III. Plurality-with-Elimination Method: D, A, C, B
- IV. Method of Pairwise Comparisons: C, B, D, A
Number of Voters: 14 10 8 4 1 1st: A C D B C 2nd: B B C D D 3rd: C D B C B 4th: D A A A A Of all of the methods discussed above which one is the best?
SLIDE 43
Fairness Criterion
SLIDE 44
Fairness Criterion
Arrow set a minimum set of requirements that a method should have:
SLIDE 45 Fairness Criterion
Arrow set a minimum set of requirements that a method should have:
◮ Non-dictatorship: There is no one voter who determines the
- utcome of every election.
SLIDE 46 Fairness Criterion
Arrow set a minimum set of requirements that a method should have:
◮ Non-dictatorship: There is no one voter who determines the
- utcome of every election.
◮ Universality: Each election has a unique outcome.
SLIDE 47 Fairness Criterion
Arrow set a minimum set of requirements that a method should have:
◮ Non-dictatorship: There is no one voter who determines the
- utcome of every election.
◮ Universality: Each election has a unique outcome. ◮ Non-imposition: Every election outcome is possible.
SLIDE 48 Fairness Criterion
Arrow set a minimum set of requirements that a method should have:
◮ Non-dictatorship: There is no one voter who determines the
- utcome of every election.
◮ Universality: Each election has a unique outcome. ◮ Non-imposition: Every election outcome is possible.
Majority Criterion: A majority candidate should always be the winner.
SLIDE 49 Fairness Criterion
Arrow set a minimum set of requirements that a method should have:
◮ Non-dictatorship: There is no one voter who determines the
- utcome of every election.
◮ Universality: Each election has a unique outcome. ◮ Non-imposition: Every election outcome is possible.
Majority Criterion: A majority candidate should always be the winner. Monotonicity Criterion: If candidate X is the winner, then X would still be the winner had a voter ranked X higher in his preference ballot.
SLIDE 50 Fairness Criterion
Arrow set a minimum set of requirements that a method should have:
◮ Non-dictatorship: There is no one voter who determines the
- utcome of every election.
◮ Universality: Each election has a unique outcome. ◮ Non-imposition: Every election outcome is possible.
Majority Criterion: A majority candidate should always be the winner. Monotonicity Criterion: If candidate X is the winner, then X would still be the winner had a voter ranked X higher in his preference ballot.
◮ Unanimity: If every voter prefers one candidate over another,
the outcome will reflect that.
SLIDE 51 Fairness Criterion
Arrow set a minimum set of requirements that a method should have:
◮ Non-dictatorship: There is no one voter who determines the
- utcome of every election.
◮ Universality: Each election has a unique outcome. ◮ Non-imposition: Every election outcome is possible. ◮ Unanimity: If every voter prefers one candidate over another,
the outcome will reflect that.
◮ Independence-of-irrelevant-alternatives (IIA) Criterion: If
candidate X is the winner then X would still be the winner had one or more of the losing candidates not been in the race.
SLIDE 52 Fairness Criterion
Arrow set a minimum set of requirements that a method should have:
◮ Non-dictatorship: There is no one voter who determines the
- utcome of every election.
◮ Universality: Each election has a unique outcome. ◮ Non-imposition: Every election outcome is possible. ◮ Unanimity: If every voter prefers one candidate over another,
the outcome will reflect that.
◮ Independence-of-irrelevant-alternatives (IIA) Criterion: If
candidate X is the winner then X would still be the winner had one or more of the losing candidates not been in the race. Condorcet Criterion: A Condorcet candidate (i.e. a candidate that beats each of the other candidate in a pairwise comparison) should always be the winner.
SLIDE 53 Fairness Criterion
Arrow set a minimum set of requirements that a method should have:
◮ Non-dictatorship: There is no one voter who determines the
- utcome of every election.
◮ Universality: Each election has a unique outcome. ◮ Non-imposition: Every election outcome is possible. ◮ Unanimity: If every voter prefers one candidate over another,
the outcome will reflect that.
◮ Independence-of-irrelevant-alternatives (IIA) Criterion: If
candidate X is the winner then X would still be the winner had one or more of the losing candidates not been in the race.
SLIDE 54
Arrow’s Impossibility Theorem
For elections involving three or more candidates, a method for determining election results that is always fair is mathematically impossible.
SLIDE 55
Arrow’s Impossibility Theorem
For elections involving three or more candidates, a method for determining election results that is always fair is mathematically impossible. C = set of all candidates
SLIDE 56
Arrow’s Impossibility Theorem
For elections involving three or more candidates, a method for determining election results that is always fair is mathematically impossible. C = set of all candidates L(C) = the set of all full linear orderings of candidates
SLIDE 57
Arrow’s Impossibility Theorem
For elections involving three or more candidates, a method for determining election results that is always fair is mathematically impossible. C = set of all candidates L(C) = the set of all full linear orderings of candidates P(C) = set of all preference schedules
SLIDE 58 Arrow’s Impossibility Theorem
For elections involving three or more candidates, a method for determining election results that is always fair is mathematically impossible. C = set of all candidates L(C) = the set of all full linear orderings of candidates P(C) = set of all preference schedules = L(C) × L(C) × · · · × L(C)
= L(C)N for N = number of voters
SLIDE 59 Arrow’s Impossibility Theorem
For elections involving three or more candidates, a method for determining election results that is always fair is mathematically impossible. C = set of all candidates L(C) = the set of all full linear orderings of candidates P(C) = set of all preference schedules = L(C) × L(C) × · · · × L(C)
= L(C)N for N = number of voters social welfare function: F : P(C) → L(C) (b1, b2, . . . , bN) → bW
SLIDE 60 Arrow’s Impossibility Theorem
For elections involving three or more candidates, a method for determining election results that is always fair is mathematically impossible. C = set of all candidates L(C) = the set of all full linear orderings of candidates P(C) = set of all preference schedules = L(C) × L(C) × · · · × L(C)
= L(C)N for N = number of voters social welfare function: F : P(C) → L(C) (b1, b2, . . . , bN) → bW
Number of Voters: 14 10 8 4 1 1st: A C D B C 2nd: B B C D D 3rd: C D B C B 4th: D A A A A → 1st: C 2nd: D 3rd: B 4th: A
SLIDE 61 Proof of Arrow’s Impossibility Theorem
social welfare function: F : P(A) → L(A) (b1, b2, . . . , bN) → bW
◮ Non-dictatorship: There is no one voter who determines the
- utcome of every election.
◮ Universality: Each election has a unique outcome. ◮ Non-imposition: Every election outcome is possible. ◮ Unanimity: If every voter prefers one candidate over another,
the outcome will reflect that.
◮ Independence-of-irrelevant-alternatives (IIA) Criterion: If
candidate X is the winner then X would still be the winner had one or more of the losing candidates not been in the race.
SLIDE 62
Proof of Arrow’s Impossibility Theorem
social welfare function: F : P(C) → L(C) (b1, b2, . . . , bN) → bW
◮ Non-dictatorship: F is not a projection. ◮ Universality: F is a well-defined function. ◮ Non-imposition: F is surjective. ◮ Unanimity: If A is ranked higher than B for all ballots bi for
i ∈ {1, . . . , N} then A should be ranked higher than B in F(b1, . . . , bN).
◮ Independence-of-irrelevant-alternatives (IIA) Criterion: For
two preference schedules (b1, . . . , bN) and (c1, . . . , cN) if the candidates A and B have the same order in bi as in ci such that for all i, then A and B have the same order in F(b1, . . . , bN) and F(c1, . . . , cN).
SLIDE 63
Proof of Arrow’s Impossibility Theorem
social welfare function: F : P(C) → L(C) (b1, b2, . . . , bN) → bW
◮ Non-dictatorship: F is not a projection. ◮ Universality: F is a well-defined function. ◮ Non-imposition: F is surjective. ◮ Unanimity: If A is ranked higher than B for all ballots bi for
i ∈ {1, . . . , N} then A should be ranked higher than B in F(b1, . . . , bN).
◮ Independence-of-irrelevant-alternatives (IIA) Criterion: For
two preference schedules (b1, . . . , bN) and (c1, . . . , cN) if the candidates A and B have the same order in bi as in ci such that for all i, then A and B have the same order in F(b1, . . . , bN) and F(c1, . . . , cN).
SLIDE 64
Proof of Arrow’s Impossibility Theorem
social welfare function: F : P(C) → L(C) (b1, b2, . . . , bN) → bW
◮ Non-dictatorship: F is not a projection. ◮ Universality: F is a well-defined function. ◮ Non-imposition: F is surjective. ◮ Unanimity: If A is ranked higher than B for all ballots bi for
i ∈ {1, . . . , N} then A should be ranked higher than B in F(b1, . . . , bN).
◮ Independence-of-irrelevant-alternatives (IIA) Criterion: For
two preference schedules (b1, . . . , bN) and (c1, . . . , cN) if the candidates A and B have the same order in bi as in ci such that for all i, then A and B have the same order in F(b1, . . . , bN) and F(c1, . . . , cN).
SLIDE 65
Proof of Arrow’s Impossibility Theorem
social welfare function: F : P(C) → L(C) (b1, b2, . . . , bN) → bW
◮ Non-dictatorship: F is not a projection. ◮ Universality: F is a well-defined function. ◮ Non-imposition: F is surjective. ◮ Unanimity: If A is ranked higher than B for all ballots bi for
i ∈ {1, . . . , N} then A should be ranked higher than B in F(b1, . . . , bN).
◮ Independence-of-irrelevant-alternatives (IIA) Criterion: For
two preference schedules (b1, . . . , bN) and (c1, . . . , cN) if the candidates A and B have the same order in bi as in ci such that for all i, then A and B have the same order in F(b1, . . . , bN) and F(c1, . . . , cN). Then show that a social welfare function F cannot consistently share all these properties!
SLIDE 66
Hope?
Arrow’s Impossibility Theorem For elections involving three or more candidates, a method for determining election results that is always meets all of Arrow’s fairness criteria is mathematically impossible. That this does not mean that every election is unfair or that every voting method is equally bad, nor does it mean that we should stop trying to improve the quality of our voting experience!
SLIDE 67
Hope?
Arrow’s Impossibility Theorem For elections involving three or more candidates, a method for determining election results that is always meets all of Arrow’s fairness criteria is mathematically impossible. That this does not mean that every election is unfair or that every voting method is equally bad, nor does it mean that we should stop trying to improve the quality of our voting experience! Do any of these criteria seem fishy?
SLIDE 68 Hope?
Arrow’s Impossibility Theorem For elections involving three or more candidates, a method for determining election results that is always meets all of Arrow’s fairness criteria is mathematically impossible. That this does not mean that every election is unfair or that every voting method is equally bad, nor does it mean that we should stop trying to improve the quality of our voting experience! Do any of these criteria seem fishy? People have considered weakening IIA and investigating
SLIDE 69
Thank You! math.umn.edu/∼kling202
Bangor Daily News, “Poliquin sues Dunlap to stop ranked-choice count in Maine’s 2nd District”: http://bangordailynews.com/2018/11/13/politics/poliquin-sues- dunlap-to-stop-ranked-choice-count-in-maines-2nd- district/? ga%253D2.257568523.1649929019.1542033437- 1922745084.1494327202 CNN 2016 Election Results: https://www.cnn.com/election/2016/results Radio Lab “Tweak the Vote”: https://www.wnycstudios.org/shows/radiolab