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Partisan Gerrymandering Gary King Institute for Quantitative Social Science Harvard University (talk at Brookline High School, 2/15/2011) Gary King (Harvard) 1 / 23
Partisan Gerrymandering
Gary King
Institute for Quantitative Social ScienceHarvard University
(talk at Brookline High School, 2/15/2011)
Gary King (Harvard) 1 / 23
The Most Predictably Conflictual Issue
Suppose you work hard,
graduate from BHS, go to a great college,get a graduate degree, run for political office, and get elected
You’re a respected member of the Massachusetts legislature!
Can you think of an issue that would cause you to lose your temper,have a fist fight with other legislators, or act in unethical ways?
Can you think of the most conflictual form of regular politics in theUS over the last 200 years?
Can you think of an issue about to cause a big ruckus?
Legislative Redistricting
(Watch Carefully; We’ll have a contest to redistrict Brookline shortly!)
Gary King (Harvard) 2 / 23
The Most Predictably Conflictual Issue
Suppose you work hard,
graduate from BHS, go to a great college,get a graduate degree, run for political office, and get elected
You’re a respected member of the Massachusetts legislature!
Can you think of an issue that would cause you to lose your temper,have a fist fight with other legislators, or act in unethical ways?
Can you think of the most conflictual form of regular politics in theUS over the last 200 years?
Can you think of an issue about to cause a big ruckus?
Legislative Redistricting
(Watch Carefully; We’ll have a contest to redistrict Brookline shortly!)
Gary King (Harvard) 2 / 23
The Most Predictably Conflictual Issue
Suppose you work hard, graduate from BHS,
go to a great college,get a graduate degree, run for political office, and get elected
You’re a respected member of the Massachusetts legislature!
Can you think of an issue that would cause you to lose your temper,have a fist fight with other legislators, or act in unethical ways?
Can you think of the most conflictual form of regular politics in theUS over the last 200 years?
Can you think of an issue about to cause a big ruckus?
Legislative Redistricting
(Watch Carefully; We’ll have a contest to redistrict Brookline shortly!)
Gary King (Harvard) 2 / 23
The Most Predictably Conflictual Issue
Suppose you work hard, graduate from BHS, go to a great college,
get a graduate degree, run for political office, and get elected
You’re a respected member of the Massachusetts legislature!
Can you think of an issue that would cause you to lose your temper,have a fist fight with other legislators, or act in unethical ways?
Can you think of the most conflictual form of regular politics in theUS over the last 200 years?
Can you think of an issue about to cause a big ruckus?
Legislative Redistricting
(Watch Carefully; We’ll have a contest to redistrict Brookline shortly!)
Gary King (Harvard) 2 / 23
The Most Predictably Conflictual Issue
Suppose you work hard, graduate from BHS, go to a great college,get a graduate degree,
run for political office, and get elected
You’re a respected member of the Massachusetts legislature!
Can you think of an issue that would cause you to lose your temper,have a fist fight with other legislators, or act in unethical ways?
Can you think of the most conflictual form of regular politics in theUS over the last 200 years?
Can you think of an issue about to cause a big ruckus?
Legislative Redistricting
(Watch Carefully; We’ll have a contest to redistrict Brookline shortly!)
Gary King (Harvard) 2 / 23
The Most Predictably Conflictual Issue
Suppose you work hard, graduate from BHS, go to a great college,get a graduate degree, run for political office,
and get elected
You’re a respected member of the Massachusetts legislature!
Can you think of an issue that would cause you to lose your temper,have a fist fight with other legislators, or act in unethical ways?
Can you think of the most conflictual form of regular politics in theUS over the last 200 years?
Can you think of an issue about to cause a big ruckus?
Legislative Redistricting
(Watch Carefully; We’ll have a contest to redistrict Brookline shortly!)
Gary King (Harvard) 2 / 23
The Most Predictably Conflictual Issue
Suppose you work hard, graduate from BHS, go to a great college,get a graduate degree, run for political office, and get elected
You’re a respected member of the Massachusetts legislature!
Can you think of an issue that would cause you to lose your temper,have a fist fight with other legislators, or act in unethical ways?
Can you think of the most conflictual form of regular politics in theUS over the last 200 years?
Can you think of an issue about to cause a big ruckus?
Legislative Redistricting
(Watch Carefully; We’ll have a contest to redistrict Brookline shortly!)
Gary King (Harvard) 2 / 23
The Most Predictably Conflictual Issue
Suppose you work hard, graduate from BHS, go to a great college,get a graduate degree, run for political office, and get elected
You’re a respected member of the Massachusetts legislature!
Can you think of an issue that would cause you to lose your temper,have a fist fight with other legislators, or act in unethical ways?
Can you think of the most conflictual form of regular politics in theUS over the last 200 years?
Can you think of an issue about to cause a big ruckus?
Legislative Redistricting
(Watch Carefully; We’ll have a contest to redistrict Brookline shortly!)
Gary King (Harvard) 2 / 23
The Most Predictably Conflictual Issue
Suppose you work hard, graduate from BHS, go to a great college,get a graduate degree, run for political office, and get elected
You’re a respected member of the Massachusetts legislature!
Can you think of an issue that would cause you to lose your temper,have a fist fight with other legislators, or act in unethical ways?
Can you think of the most conflictual form of regular politics in theUS over the last 200 years?
Can you think of an issue about to cause a big ruckus?
Legislative Redistricting
(Watch Carefully; We’ll have a contest to redistrict Brookline shortly!)
Gary King (Harvard) 2 / 23
The Most Predictably Conflictual Issue
Suppose you work hard, graduate from BHS, go to a great college,get a graduate degree, run for political office, and get elected
You’re a respected member of the Massachusetts legislature!
Can you think of an issue that would cause you to lose your temper,have a fist fight with other legislators, or act in unethical ways?
Can you think of the most conflictual form of regular politics in theUS over the last 200 years?
Can you think of an issue about to cause a big ruckus?
Legislative Redistricting
(Watch Carefully; We’ll have a contest to redistrict Brookline shortly!)
Gary King (Harvard) 2 / 23
The Most Predictably Conflictual Issue
Suppose you work hard, graduate from BHS, go to a great college,get a graduate degree, run for political office, and get elected
You’re a respected member of the Massachusetts legislature!
Can you think of an issue that would cause you to lose your temper,have a fist fight with other legislators, or act in unethical ways?
Can you think of the most conflictual form of regular politics in theUS over the last 200 years?
Can you think of an issue about to cause a big ruckus?
Legislative Redistricting
(Watch Carefully; We’ll have a contest to redistrict Brookline shortly!)
Gary King (Harvard) 2 / 23
The Most Predictably Conflictual Issue
Suppose you work hard, graduate from BHS, go to a great college,get a graduate degree, run for political office, and get elected
You’re a respected member of the Massachusetts legislature!
Can you think of an issue that would cause you to lose your temper,have a fist fight with other legislators, or act in unethical ways?
Can you think of the most conflictual form of regular politics in theUS over the last 200 years?
Can you think of an issue about to cause a big ruckus?
Legislative Redistricting
(Watch Carefully; We’ll have a contest to redistrict Brookline shortly!)
Gary King (Harvard) 2 / 23
The Most Predictably Conflictual Issue
Suppose you work hard, graduate from BHS, go to a great college,get a graduate degree, run for political office, and get elected
You’re a respected member of the Massachusetts legislature!
Can you think of an issue that would cause you to lose your temper,have a fist fight with other legislators, or act in unethical ways?
Can you think of the most conflictual form of regular politics in theUS over the last 200 years?
Can you think of an issue about to cause a big ruckus?
Legislative Redistricting
(Watch Carefully; We’ll have a contest to redistrict Brookline shortly!)
Gary King (Harvard) 2 / 23
U.S. House of Representatives
Gary King (Harvard) 3 / 23
Count Everyone Apportion Seats to States
Gary King (Harvard) 4 / 23
Redistrict Within States
Gary King (Harvard) 5 / 23
Gary King (Harvard) 6 / 23
Is this fair?Texas, before redistricting
Gary King (Harvard) 7 / 23
Or is this fair?Texas, after redistricting
Gary King (Harvard) 8 / 23
(Important but Inadequate!) Standards for Fairness
1 Equal population
2 Preserving “Communities of Interest”
3 Compactness (and contiguity)
Gary King (Harvard) 9 / 23
Arizona’s 2nd Congressional District
Gary King (Harvard) 10 / 23
North Carolina’s 12nd Congressional District
Gary King (Harvard) 11 / 23
Illinois’ 4th Congressional District
Gary King (Harvard) 12 / 23
Governor Gerry’s 1812 “Gerrymander” in Massachusetts
Gary King (Harvard) 13 / 23
How many (of 4) legislative seats should each party get?
Democratic vote % in each precinct
90 40 40 40
90 40 40 40
90 40 40 40
90 40 40 40
(Average = 52.5%)
Gary King (Harvard) 14 / 23
A Republican Redistricting Plan
90 40 40 40
90 40 40 40Average
90 40 40 40
90 40 40 40
90 40 40 40
Democrats win 1 of 4 seats
Gary King (Harvard) 15 / 23
A Democratic Redistricting Plan
90 40 40 40 52.5
90 40 40 40 52.5
90 40 40 40 52.5
90 40 40 40 52.5
Average
Democrats win all 4 seats
Gary King (Harvard) 16 / 23
New Standards for Fair Redistricting
1 Equal population
2 Preserving “Communities of Interest”
3 Compactness (and contiguity)
4 Partisan symmetry (no bias)
5 Electoral responsiveness
Gary King (Harvard) 17 / 23
The Surpreme Court on Partisan Symmetry
Gary King (Harvard) 18 / 23
Fair Seats-Votes CurvesPartisan symmetry: When votes are split equally, seats are split equally
Fair, Proportional
Dem Vote Proportion
Dem
Sea
t Pro
port
ion
0.00
0.25
0.50
0.75
1.00
0.00 0.25 0.50 0.75 1.00
Fair, Responsive
Dem Vote Proportion
Dem
Sea
t Pro
port
ion
0.00
0.25
0.50
0.75
1.00
0.00 0.25 0.50 0.75 1.00
Gary King (Harvard) 19 / 23
Biased Seats-Votes CurvesPartisan Bias: When votes are split equally, seats are split unequally
Biased, Proportional
Dem Vote Proportion
Dem
Sea
t Pro
port
ion
0.00
0.25
0.50
0.75
1.00
0.00 0.25 0.50 0.75 1.00
Biased, Responsive
Dem Vote Proportion
Dem
Sea
t Pro
port
ion
0.00
0.25
0.50
0.75
1.00
0.00 0.25 0.50 0.75 1.00
Gary King (Harvard) 20 / 23
Calculating a Seats-Votes Curve
Dem Vote Proportion
Dem
Sea
t Pro
port
ion
0.00
0.25
0.50
0.75
1.00
0.00 0.25 0.50 0.75 1.00
●
●
Compute average vote and seatproportions; plot black dot
Find difference of vote averagefrom 0.5
Add difference from everydistrict’s vote (new vote average= 0.5)
See who “wins” new districtswith the adjusted votes;calculate seat proportion; plotred dot
Calculate bias (difference in seatproportion from 0.5)
Gary King (Harvard) 21 / 23
Calculating a Seats-Votes Curve
Dem Vote Proportion
Dem
Sea
t Pro
port
ion
0.00
0.25
0.50
0.75
1.00
0.00 0.25 0.50 0.75 1.00
●
●
Compute average vote and seatproportions; plot black dot
Find difference of vote averagefrom 0.5
Add difference from everydistrict’s vote (new vote average= 0.5)
See who “wins” new districtswith the adjusted votes;calculate seat proportion; plotred dot
Calculate bias (difference in seatproportion from 0.5)
Gary King (Harvard) 21 / 23
Calculating a Seats-Votes Curve
Dem Vote Proportion
Dem
Sea
t Pro
port
ion
0.00
0.25
0.50
0.75
1.00
0.00 0.25 0.50 0.75 1.00
●
●
Compute average vote and seatproportions; plot black dot
Find difference of vote averagefrom 0.5
Add difference from everydistrict’s vote (new vote average= 0.5)
See who “wins” new districtswith the adjusted votes;calculate seat proportion; plotred dot
Calculate bias (difference in seatproportion from 0.5)
Gary King (Harvard) 21 / 23
Calculating a Seats-Votes Curve
Dem Vote Proportion
Dem
Sea
t Pro
port
ion
0.00
0.25
0.50
0.75
1.00
0.00 0.25 0.50 0.75 1.00
●
●
Compute average vote and seatproportions; plot black dot
Find difference of vote averagefrom 0.5
Add difference from everydistrict’s vote (new vote average= 0.5)
See who “wins” new districtswith the adjusted votes;calculate seat proportion; plotred dot
Calculate bias (difference in seatproportion from 0.5)
Gary King (Harvard) 21 / 23
Calculating a Seats-Votes Curve
Dem Vote Proportion
Dem
Sea
t Pro
port
ion
0.00
0.25
0.50
0.75
1.00
0.00 0.25 0.50 0.75 1.00
●
●
Compute average vote and seatproportions; plot black dot
Find difference of vote averagefrom 0.5
Add difference from everydistrict’s vote (new vote average= 0.5)
See who “wins” new districtswith the adjusted votes;calculate seat proportion; plotred dot
Calculate bias (difference in seatproportion from 0.5)
Gary King (Harvard) 21 / 23
Calculating a Seats-Votes Curve
Dem Vote Proportion
Dem
Sea
t Pro
port
ion
0.00
0.25
0.50
0.75
1.00
0.00 0.25 0.50 0.75 1.00
●
●
Compute average vote and seatproportions; plot black dot
Find difference of vote averagefrom 0.5
Add difference from everydistrict’s vote (new vote average= 0.5)
See who “wins” new districtswith the adjusted votes;calculate seat proportion; plotred dot
Calculate bias (difference in seatproportion from 0.5)
Gary King (Harvard) 21 / 23
Gary King (Harvard) 22 / 23
What did we learn?
In redistricting, the rules of the game are part of the game
With partisan symmetry, math can make redistricting fair
In practice, redistricting is a mess; law suits will be filed everywhere;rules will be broken; hundreds of millions of dollars will be spent
To legislators, this is the most visible issue
Redistricting is often invisible to the public. . . but not to you!
Gary King (Harvard) 23 / 23
What did we learn?
In redistricting, the rules of the game are part of the game
With partisan symmetry, math can make redistricting fair
In practice, redistricting is a mess; law suits will be filed everywhere;rules will be broken; hundreds of millions of dollars will be spent
To legislators, this is the most visible issue
Redistricting is often invisible to the public. . . but not to you!
Gary King (Harvard) 23 / 23
What did we learn?
In redistricting, the rules of the game are part of the game
With partisan symmetry, math can make redistricting fair
In practice, redistricting is a mess; law suits will be filed everywhere;rules will be broken; hundreds of millions of dollars will be spent
To legislators, this is the most visible issue
Redistricting is often invisible to the public. . . but not to you!
Gary King (Harvard) 23 / 23
What did we learn?
In redistricting, the rules of the game are part of the game
With partisan symmetry, math can make redistricting fair
In practice, redistricting is a mess; law suits will be filed everywhere;rules will be broken; hundreds of millions of dollars will be spent
To legislators, this is the most visible issue
Redistricting is often invisible to the public. . . but not to you!
Gary King (Harvard) 23 / 23
What did we learn?
In redistricting, the rules of the game are part of the game
With partisan symmetry, math can make redistricting fair
In practice, redistricting is a mess; law suits will be filed everywhere;rules will be broken; hundreds of millions of dollars will be spent
To legislators, this is the most visible issue
Redistricting is often invisible to the public. . . but not to you!
Gary King (Harvard) 23 / 23
What did we learn?
In redistricting, the rules of the game are part of the game
With partisan symmetry, math can make redistricting fair
In practice, redistricting is a mess; law suits will be filed everywhere;rules will be broken; hundreds of millions of dollars will be spent
To legislators, this is the most visible issue
Redistricting is often invisible to the public. . . but not to you!
Gary King (Harvard) 23 / 23
