A statistics presentation I gave at work using simulation to predict election results from state-by-state polling data.

1. But first…..
Something of topical interest …
Psephology
The M&M graph…

2. Poll of polls for October 8th, 2004 - Posted October 15th, 2004
Dead Heat
Before the second and third debates, Bush's lead has dropped to less than 0.1%...
http://tis.goringe.net/pop/pollofpolls.html

3. Reweighting by Party ID?
Shifting Party Affiliation
Strong Republican
100%
Weak Republican
90%
80%
Independent
70% Republican
60%
Independent
50% Independent
40%
Independent
30% Democrat
20%
Weak Democrat
10%
0%
Strong Democrat
2
6
0
4
8
2
6
0
4
8
2
6
0
'5
'5
'6
'6
'6
'7
'7
'8
'8
'8
'9
'9
'0
Year

4. “Dewey Beats Truman”
Chicago Tribune, Nov 3, 1948
Sources of bias:
• “distribution of telephones favored wealthy
Dewey voters rather than poor Truman
supporters”
• “the pollsters stopped polling two weeks or more
before the election.”
• Convenience Sampling

5. Golden Age of Polling?
• >95% Households have a telephone
Easy to get random sample
• Until recently: good response
• Now: caller id, answering machines, etc.
30% response rate
Cell Phones: No landline èYounger, Democratic

6. Online Polling?

7. Demographics
• "As people do better, they start voting
like Republicans--unless they have too
much education and vote Democratic,
which proves there can be too much of a
good thing." --Karl Rove

8. Electoral College Map

9. Electoral College Approach
KERRY ELECTORAL VOTE PROJECTIONS
from State-Level Poll Data
18-Oct-2004
Total
number of Electoral
states Votes
Bush > 55% 15 110 Bush total:
Bush 50-55% 12 146 256
Kerry 50-55% 15 187 Kerry total:
Kerry > 55% 9 95 282
51 538
polls used beginning ending
in estimate: 10/7/2004 10/12/2004

10. Basis for Simulation
State EV K.share SD
AL 9 44.3% 0.7%
AK 3 37.0% 1.2%
AZ 10 46.1% 3.2%
AR 6 53.1% 3.1%
CA 55 54.6% 2.8%
CO 9 46.8% 2.2%
CT 7 55.1% 2.7%
DE 3 54.5% 2.4%
DC 3 89.5% 0.7%

11. Simulate Elections
1 Random Electoral Votes
Rand# SD Mean Normal Kerry Bush
AL 0.396 0.73% 44.35% -5.84% 9
AK 0.281 1.20% 37.03% -13.66% 3
AZ 0.314 3.15% 46.08% -5.44% 10
AR 0.244 3.12% 53.15% 0.98% 6
CA 0.105 2.78% 54.63% 1.14% 55
CO 0.441 2.19% 46.76% -3.56% 9
CT 0.113 2.70% 55.15% 1.87% 7
DE 0.44 2.40% 54.50% 4.13% 3
DC 0.474 0.73% 89.49% 39.44% 3
22-Jul 4-Aug 30-Aug 2-Sep 7-Sep
Elect Wins 76.0% 73.0% 56.4% 37.0% 39.2%
Loses 23.6% 26.1% 42.2% 61.2% 59.7%
Ties 0.4% 0.9% 1.4% 1.8% 1.1%
Odds 3.22to1 2.80to1 1.34to1 0.60to1 0.66to1

12. Estimating States (1)
• Historical data:
Compare state outcomes vs national
• Current data:
Adjust national poll by historical difference
• Combine with recent state polls
Example: http://www.mydd.com/story/2004/5/28/115448/006

13. Estimating States (2)
Election data:
1980-2000 (6 elections) state vote counts
For pair of states (2550 pairs):
Regress each states vote on all other states
For each available poll:
Predict votes in all other states
For each state:
Use the median of predicted votes
www.pollkatz.homestead.com/files/kerryEVproj.htm

14. Forecasting Models
Predict Vote from: Economic conditions,
social climate, incumbency, “party fatigue”,
etc., etc.
Limited by: Too little data
Result: perfect predictions of past elections
Explanatory, not predictive

15. Bread & Peace Equation
14
Votet = α + β1 ∑ λ j Δ ln Rt − j + β 2 CUM KIAt
j =0
Real Income Growth and the Two-Party Vote Share of the
Votes as a function of: Incumbent Party's Presidential Candidate
%
65
• Income growth 1972
60 1984 1964
• War Casualties 1956
Two-party vote share
Vietnam
55
2004: Predicts ~53% Bush 1996 1988
1960
50 Korea
Explanatory, not predictive! 1976
1968
1992
45
(Who’s income?) 1980 1952
40
-1 -0.5 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 %
Weighted-average growth of real disposable personal income per
capita during the presidential term

16. Incumbent Advantage or
Disadvantage?
• Forecasting models:
Incumbent advantage
• Final Polls vs. Final Votes:
Incumbent disadvantage
Apparently, undecideds lean toward
challenger (at about 2:1)

17. My Favorite Forecasting Model
Electability = 4P - V - S + R + 9G
+ 95DCI + 95GEN + 95NUC
• Elections since 1932
• Predicts all elections since 1932
• Developed using stochastic trials
(i.e., guessing until something worked)
• Source: Annuals of Improbable Results
2004: Bush, 70; Kerry -20
http://members.bellatlantic.net/~vze3fs8i/air/pres2004.html

18. Another Favorite
Washington Redskins, Last home game prior to election
Redskins Win è Incumbent wins
Redskins Lose è Incumbent loses
• True for entire history of Washington Redskins
(15 elections)
(1932 & earlier: Boston Braves, no predictive power)
• October 31, 2004: vs Green Bay
Not anymore
28 to 14 defeat, favor Kerry

19. University of Iowa's Electronic Market
http://128.255.244.60/graphs/graph_Pres04_WTA.cfm

20. Obligatory Bayesian Methods
A Bayesian Truth Serum for Subjective Data. Prelec,
Drazen. Science, Vol 306, Issue 5695, 462-466 ,
15 October 2004
• Reward based system
• Respondents “compete”
• Counterbalances tendency to agree with
perceived majority
• Best: large samples, rational participants

21. Bayesian Truth Serum
Example:
Q1: Do you prefer painting A or B?
Q2: Which would others prefer?
• Compute Information score+prediction score
using sums of logarithms for each respondant and etc etc
• Truth Telling is Bayesian Nash equilibrium (I.e.,
reduced payoffs for anything else)
• Does it work? When? For who? For only Bayesians?
What about frequentists? Under what conditions? Cost? Etc...
• A work in progress