2008 Election Model Methodology: Assumptions, Calculations and a Challenge
This post will describe the essential methodology used in
the 2008 Election Model for calculating the expected electoral vote and win
probability. It will show why the 99% Obama win probability calculation is mathematically correct
assuming a) the election is held today b) is fraud-free and c) the latest state
polls represent true voter preference. Important issues such as cell-phone
users, RV vs.
Fivethirtyeight.com has a great site with a tremendous
amount of information. But their win probabilities are much too low; it’s
mathematically incorrect to derive a 75% win probability to a 311-227 EV vote
split. The win probability is
incompatible with the split, as is seen from running a 5000 trial
Those who compare
The betting payoffs are based on the recorded vote – even if
it was stolen. On Election Day 2004, Kerry was leading the
There are some critics who skip over my standard caveats, much less the analysis: The Election Model does not attempt to predict the election results months in advance of the election, as do most academic models. It is designed to calculate the expected electoral vote winner assuming a) the election is held today and b) is fraud-free. The model calculates the effects of uncounted and switched vote scenarios on Obama’s popular and electoral vote while other models don’t even mention election fraud. But election fraud is not the issue here; the objective is to explain why the Election Model produces such a high win probabilities.
Projecting state vote shares and win probabilities
The latest state poll is used to project the 2-party vote share. Based on the projection, the state win probability is calculated. To project the state vote, the Election Model allocates undecided voters (UVA) – a simple calculation. But we don’t want to rely on a single UVA estimate; the model calculates the projected vote over a range of scenarios -from 40-80% with 60% as the base case. I leave it to the reader to choose whatever UVA he/she feels comfortable with.
Since Obama has 53% of the 2-party
national poll, it is not unreasonable to assume that he will get 60% or more of
the undecided vote. Obama can be considered the
challenger since McCain is running for the third Bush term. Pollsters typically
assign 75-90% of the undecided vote to the challenger. In 2004,
The national polls are more current than the states. Since Obama has a 53% 2-party share right now, it is to be expected that the state polls will climb. Since June, there has been a 0.57 correlation between the national and state polls.
If Obama’s projected 2-party vote share is V, then his state win probability is: calculated by the Excel formula:
P= normdist (V, 0.50, MoE/1.96, true). The Margin of Error is set to 4% for a typical state poll of 600 sample size.
That’s it. There should be no argument as to the mathematics.
Calculating the expected electoral vote and win probability
The expected state EV
is the state win probability times the electoral vote. If the probability is
50% and the state has 20 EV, then Obama gets 10 and
McCain gets 10. Now just add up the 51
expected EVs to get the Total Expected EV. So the
math is exceedingly simple. The tricky part is projecting the state vote shares
starting with the latest polls. The Election Model applies the UVA to derive
the projected 2-party vote. The 51 state win probabilities are input to a 5000
How does fivethirtyeight.com do it? We know thatelectoral-vote.com and RCP just add up the electoral vote based on who is ahead in the latest poll (average). But that can be misleading. What if McCain (or Obama) leads by 51-49% in 5 states with 100 EV? Electoral-vote.com and RCP would just give all 100 electoral votes to the leader. This is incorrect since there is no accounting for the polling spread. The probability is 31% that the trailing candidate will win the state.
The total EV is just the sum of the expected state EVs. If you agree with the state win probabilities, then the expected Electoral vote is a no-brainer.
The electoral vote win probability is simply the number of
Here’s a challenge to those who have criticized the 2008 Election Model’s win probability calculations. Compare the methodology to fivethirtyeight. But be specific. What was the 2004 fivethirtyeight projection? The Election Model correctly projected that Kerry would win the True Vote with 99% win probability - just like Obama. Of course, those who still believe that Bush won legitimately will never be convinced.
The 2004 Election Model
It’s hard to believe. But the same naysayers have been using the same old, discredited arguments for four years in their fruitless attempts to cast doubt on the 2004 exit polls which indicated that Kerry won the election.
The final 2004 Election Model projected that Kerry would win 51.8% of the 2-party vote with an expected 337 EV. The unadjusted aggregate exit poll (WPE) indicated that Kerry won 52.5%. The Kerry winning states totaled 337 EV.
1) One in 7 (14.63%) Gore 2000 voters defected to Bush in 2004.
The NEP reported 8% (10% in the Final).
2) Kerry won just 52.90% of DNV (new voters and others who did not vote in 2000).
The NEP reported 57% (54% in the Final).
3) Just 7.20% of Bush 2000 voters defected to Kerry.
The NEP reported 10% (9% in the Final).
On the other hand, the True Vote model, which used feasible weights and plausible vote shares, determined that Kerry won by 52.6-46.4%.
The assumptions were:
1) 0.87% annual mortality
2) 95% turnout of Gore, Bush and Other 2000 voters in 2004
3) 125.74m total votes were cast (Census) in 2004
4) 12:22am NEP vote shares
True Vote Model Bush Win Scenario
Pct Kerry Bush Other Pct Kerry Bush Other
DNV 21.49% 57% 41% 2% 21.72% 52.90% 46.50% 0.60%
Gore 38.23% 91% 8% 1% 37.84% 84.83% 14.63% 0.54%
Bush 37.83% 10% 90% 0% 37.44% 7.20% 92.31% 0.49%
Other 2.45% 71% 21% 8% 3.00% 65.90% 18.10% 16.00%
Share 100.0% 52.56% 46.43% 1.01% 100.0% 48.26% 50.74% 1.00%
Votes Kerry Bush Other Votes Kerry Bush Other
DNV 27.02 15.40 11.08 0.54 26.56 14.05 12.35 0.16
Gore 48.07 43.74 3.85 0.48 46.28 39.26 6.77 0.25
Bush 47.57 4.76 42.81 0.00 45.79 3.30 42.27 0.22
Other 3.08 2.19 0.65 0.25 3.67 2.42 0.66 0.59
Total 125.74 66.09 58.38 1.27 122.30 59.02 62.05 1.22
Which scenario are we to believe: the implausible 14.63% Gore defection rate or the mathematically impossible 43 Bush/ 37 Gore weights? Was the exit poll match to the recorded vote based on a) plausible 37.84 Gore/ 37.44% Bush weights and an implausible 14.63% Gore defection rate, or b) the Final NEP impossible 43 Bush/ 37% Gore weights and plausible (8-10%) Gore defection rate?
They said the reason for the mass defection of Gore voters was due to a long-term bandwagon effect: former Gore voters wanted to associate with the “winner”, Bush. But “false recall” is not a plausible explanation since a) Gore won by 540,000 votes, b) according to the pristine 12:22am NEP, Kerry captured 91% of Gore voters and 10% of Bush voters, c) Bush had a 48.5% approval rating on Election Day, d) false recall is not applicable to pre-election polls and e) the pre-election polls matched the exit polls.
Why would Gore voters want to be associated with Bush? Even if returning Gore voters lied about their vote in 2000, it’s irrelevant. What is relevant is a) their factual 2000 recorded Gore vote and b) that 91% said they just voted for Kerry. We use this factual data to compute feasible and plausible weights by adjusting the 2000 recorded vote for mortality and estimated 2004 turnout.
False recall cannot be used as an explanation to explain the other demographic weightings. In the 12:22am NEP, 13047 respondents were asked who they just voted for – and Kerry won. But only 3200 respondents were asked how they voted in 2000. Kerry must have also won the 10,000 who were not asked how they voted in 2000. This fact alone totally contradicts the “false recall” argument. Why would respondents lie to the exit pollsters and claim to have voted for Kerry if they voted for Bush? Did they also lie about their gender? Kerry won the Gender demographic by 50.78-48.22%.
GENDER Weight Kerry Bush Other
Male 46% 47% 52% 1%
Female 54% 54% 45% 1%
Share 100% 50.78% 48.22% 1.00%
Votes 122.3 62.10 58.97 1.22
The model calculates the True Vote for all elections since 1988.
For the 2004 election, the data consists of:
1) Census: 125.7m votes cast in 2004 vs. 122.3m recorded; 3.4m (2.74%) uncounted
2) Census: 110.8m votes cast in 2000 vs. 105.4m recorded; 5.4m (4.86%) uncounted
3) Annual voter mortality: 1.22% (4.88% over 4 years)
1) 12:22am NEP vote shares
2) 2000 voter turnout in 2004: 95%
3) 75% of uncounted votes to Gore and Kerry
Voted Recd Unctd Cast Died Alive
Gore 51.00 4.04 55.04 2.72 52.32
Bush 50.46 1.08 51.53 2.48 49.06
Other 3.96 0.27 4.23 0.21 4.02
Total 105.42 5.38 110.8 5.41 105.39
Turnout Voted Weight Kerry Bush Other
DNV - 25.61 20.4% 57% 41% 2%
Gore 95% 49.70 39.5% 91% 8% 1%
Bush 95% 46.60 37.1% 10% 90% 0%
Other 95% 3.82 3.0% 64% 17% 19%
Total 100.1 125.7 100% 53.23% 45.39% 1.38%
66.94 57.07 1.74
Here is a challenge for those who still believe that Bush won by 3 million votes:
Download the The Election Calculator Model and construct a 2004 Bush win scenario.