Section 1 2 Plurality Instant Runoff and Hare

Section 1. 2 Plurality, Instant Runoff, and Hare 1. 2 Plurality, IRV, and Hare

Who should win? 1. A 2. B 3. C 4. D 10 A D C B 1. 2 9 B C D A 5 C B D A 1 D C A B Plurality, IRV, and Hare 2

10 A D C B Ideas 1. 2 Plurality, IRV, and Hare 9 B C D A 5 C B D A 1 D C A B 3

Voting Method 1 Plurality Most Votes Wins 1. 2 Plurality, IRV, and Hare 4

• “Plurality” = More votes than anyone else . (Simply look along the top row) 35 33 32 A C B B B C C • Plurality Winner is A A • Is there a majority winner? • Plurality is the only voting method that may elect someone disliked by of the voters 1. 2 Plurality, IRV, and Hare 5

Who wins using Plurality? 1 1 1 A C E D B B D C B E A B B C B A C B B C A B C C A A A E D D C E E E A D E D C E E D A D D E E D C D 1. A 2. B 3. C 4. D 5. E 1. 2 Plurality, IRV, and Hare 6

• Plurality is also known as “Winner-Take-All” • In presidential elections all the electoral votes in 48/50 states are awarded to the Plurality winner “Chads” 1. 2 Plurality, IRV, and Hare 7

Which is correct? 1. If you have a majority of the votes then you have a plurality 2. If you have a plurality then you have a majority of the votes 3. Both statements are true 4. Both statements are false 1. 2 Plurality, IRV, and Hare 8

Who wins using Plurality? 1. A 2. B 3. C 4. D 8 9 6 4 B A C C C D B D A C A B D A An extreme case 1. 2 Plurality, IRV, and Hare 9

Plurality High School Class Rank A school ranks its students by the number of A’s they receive Who would be ranked higher? Hildegard: Hortense: 1. 2 Plurality, IRV, and Hare 10

Plurality - For Better or Worse • Most researchers believe that Plurality does the job of picking a winner • It is still widely used for important elections in the United States, Canada, the United Kingdom, and India • And by the faculty in our College of Arts and Sciences 1. 2 Plurality, IRV, and Hare . 11

Plurality - Advantages 1. Easy to 2. Easy to 1. 2 Plurality, IRV, and Hare 12

Plurality - Disadvantages 8 7 3 B A C B B 2. Vo Ap A A Cli C C 1. Sm Why bother? My guy (C) hasn’t got a chance. I’m outta here 1. 2 Plurality, IRV, and Hare 13

First disadvantage is the big problem with Plurality. How can we prevent a small clique from winning? 1. Keep having elections until someone gets a majority 2. Reduce the field to 2 candidates 3. You can’t prevent it 4. Other Animation 1. 2 Plurality, IRV, and Hare 14

Animation showed Traditional Runoff Election Very common - Two separate elections separated by weeks/months Drawbacks • Expensive • Longer campaigns • Different voting group for 2 nd election 1. 2 Plurality, IRV, and Hare 15

How could we conduct a Runoff “instantly” using only this preference schedule? 20 19 15 10 A B C D D D B C C C D B B A A A 1. 2 Plurality, IRV, and Hare 16

Voting Method 2 Instant Runoff Voting (IRV) Algorithm • all candidates . . . • “Re-tally” the . • The candidate with votes wins 1. 2 Plurality, IRV, and Hare 17

What is an “algorithm”? • Arabic for “calculate” • Definition: A precise set of rules specifying how to solve some problem • Examples – Divide 232 by 17 – Shampoo 1. 2 Plurality, IRV, and Hare 18

Animation of the IRV algorithm First Tally Eliminate 15 9 4 3 2 A B C D E B E E B A C A B C C D D A E B E C D A D Re-Tally wins 1. 2 to Plurality, IRV, and Hare . 19

Who wins using IRV (and how many votes did the winner get? ) 1. 2. 3. 4. 5. 6. 7. 8. A – 10 A – 15 B – 10 B – 12 C – 10 C – 15 D – 12 D – 17 10 7 5 5 B D C A A C D A D D C B B B 1. 2 Plurality, IRV, and Hare 20

Different voting methods can produce different winners in the same election 1. True 2. False 1. 2 Plurality, IRV, and Hare 21

10 7 5 5 B D C A A C D A D D C B B B IRV winner Plurality winner . . Important Theme #1 1. 2 Plurality, IRV, and Hare 22

If candidate A has a majority of the firstplace votes, A will always win using IRV 1. True 2. False 3. Can’t tell 1. 2 Plurality, IRV, and Hare 23

Instant Runoff - Advantages Ma 2. Ch 3. L 4. 98 3 A B C 1. 100 B C A C B A W er L P Fewer Per Att 5. 1. 2 Plurality, IRV, and Hare 24

Which candidate has a legitimate complaint with IRV? 1. A 2. B 3. C 4. D 5. No one 100 98 A B C C D D B 1. 2 A 97 C A D 2 D C A B B Plurality, IRV, and Hare 25

IRV – Disadvantage French Presidential Election - 2002 Election 1. 2 Plurality, IRV, and Hare 26

How to prevent strong 3 rd, 4 th, … place candidates from being eliminated in the first round? 1. Eliminate all but the top 3 vote getters and re-tally 2. Eliminate all but the top 4 vote getters and re-tally 3. Eliminate the lowest vote getter. Retally. Again, eliminate lowest votegetter. Re-tally. Etc. etc. 4. You can’t prevent it 1. 2 Plurality, IRV, and Hare 27

http: //video. google. com/videoplay? docid=13853515 42097864075&q=musical+chairs&hl=en 1. 2 Plurality, IRV, and Hare 28

The video hints at a new voting method. Explain how it works with this preference schedule 20 19 15 10 A B C D D D B C C C D B B A A A 1. 2 Plurality, IRV, and Hare 29

Voting Method 3 Hare Algorithm • • the Re-tally the process, each time eliminating the • The one with the . Repeat this. Eventually there will be only • . . wins 1. 2 Plurality, IRV, and Hare 30

Animation using Hare 8 9 6 B A C D B C A B D Tally 1 3 A Re-Tally wins 1. 2 to Plurality, IRV, and Hare . 31

Who wins using Hare? (and determine how many votes the winner gets) 1. A – 23 2. A – 35 3. B – 18 4. B – 35 5. C – 34 17 A C D 6. C – 37 B A D B 7. D – 28 8. D – 45 1. 2 12 B C D 6 C A B 16 D C A Plurality, IRV, and Hare 32

If there are 3 candidates IRV and Hare 1. Always choose the same winner 2. Never choose the same winner 3. Sometimes choose the same winner 4. Can’t tell 1. 2 Plurality, IRV, and Hare 33

If A has a majority of the first-place votes, A will always win using Hare 1. True 2. False 3. Can’t tell 1. 2 Plurality, IRV, and Hare 34

Hare Method – Advantages 1. M 2. Co 3. Fewer P 4. En W ve A V 1. 2 T Plurality, IRV, and Hare 35

Hare Method – Disadvantages 1. D to E 1. 2 Plurality, IRV, and Hare 36

Who wins using Plurality? 1. A 2. B 3. 19 B D C A 15 C B D A 10 D C B A C 4. 20 A D C B D 1. 2 Plurality, IRV, and Hare 37

Who wins using IRV? 1. A 2. B 3. 19 B D C A 15 C B D A 10 D C B A C 4. 20 A D C B D 1. 2 Plurality, IRV, and Hare 38

Who wins using Hare? 1. A 2. B 3. 19 B D C A 15 C B D A 10 D C B A C 4. 20 A D C B D 1. 2 Plurality, IRV, and Hare 39

OK, who wins? (Sorry, no questions on this one) 35 33 32 1. A 2. B 3. C 4. A C B B B C C A A I don’t know 1. 2 Plurality, IRV, and Hare 40

If you wanted candidate A to win which voting method would you choose? 1. Plurality 17 A D C B 19 B D A C 21 C B A D 10 D A B C 2. Run off 3. Hare 1. 2 Plurality, IRV, and Hare 41

If you wanted candidate B to win which voting method would you choose? 1. Plurality 17 A D C B 19 B D A C 21 C B A D 10 D A B C 2. Run off 3. Hare 1. 2 Plurality, IRV, and Hare 42

If you wanted candidate C to win which voting method would you choose? 1. Plurality 17 A D C B 19 B D A C 21 C B A D 10 D A B C 2. Run off 3. Hare 1. 2 Plurality, IRV, and Hare 43

End of 1. 2 Plurality, IRV, and Hare

2000 Presidential Election Florida’s Famous “Hanging Chads” 1. Bush defeats Gore by 537 votes (out of 5, 800, 000 cast) 2. Wins ALL electoral votes in the state 3. Bush becomes President 1. 2 Plurality, IRV, and Hare 45

Plurality - An Extreme Case The Likud Party United Torah Judaism The Center Party Kadima Aguddat Israel Herut Degel Hattorah Centrist Party Takes Shape Ariel Sharon Forms New Political Party Gahal Ahdut Ha'avodah Mapai The Israeli Communist Party General Zionists/Liberal Party Gesher Democratic Movement for Change Arab Democratic Party Democratic Choice Hadash Arab Movement for Change Citizen's Rights Movement Kach The Labor Party 1. 2 Plurality, IRV, and Hare United Arab List 46

Election 1 A B C D E 10 9 4 3 2 Election 2 1. 2 Plurality, IRV, and Hare 47

French Presidential Election 2002 Candidates Votes 1 st round % Votes 2 nd round % Jacques Chirac 5, 665, 855 19. 88% 25, 537, 956 82. 21% Jean-Marie Le Pen 4, 804, 713 16. 86% 5, 525, 032 17. 79% Lionel Jospin 4, 610, 113 16. 18% François Bayrou 1, 949, 170 6. 84% Arlette Laguiller 1, 630, 045 5. 72% Jean-Pierre Chevènem ent 1, 518, 528 5. 33% Noël Mamère Olivier Besancen ot 1. 2 Plurality, IRV, and Hare 48

Meta - Material 1. 2 Plurality, IRV, and Hare