An Electoral Vote Forecast Formula: Simulation or Meta-analysis Not Required

An Electoral Vote Forecast Formula

Link to source tables and graphs:
http://richardcharnin.wordpress.com/2011/10/31/a-simple-expected-electoral-vote-formula-simulation-or-meta-analysis-not-required/

It is interesting to note that neither a simulation or a meta-analysis is required to calculate the expected electoral vote. Of course the individual state projections will depend on the forecasting method used. But the projection method is not the main issue here; it’s how the associated win probabilities are used to calculate the expected EV, win probability and frequency distribution.

Calculating the expected electoral vote is a three-step process:
1. Project the 2-party vote share V(i) for each state(i) as the sum of the final pre-election poll share PS(i) and the undecided voter allocation UVA(i):
V(i)= PS(i) + UVA(i)

2. Calculate the probability P(i) of winning each state given the margin of error (95% confidence):
P(i) = NORMDIST (V(i), 0.5, MoE/1.96, true)

3. Calculate the expected electoral vote EV. It is the product sum of the state win probabilities and the electoral votes:
EV = sum (P(i) * EV(i)), for i = 1,51 states

The challenger is expected to win the majority (60-90% UVA) of the undecided vote, depending on incumbent job performance. Gallup allocated 90% of undecided voters to Kerry in their final projection, pollsters Zogby and Harris: 75-80%. The National Exit Poll indicated that 65% of undecided voters broke for Kerry. Bush had a 48% approval rating on Election Day.

After calculating the individual state probabilities, we can calculate the EV win probability. The best, most straightforward method is Monte Carlo simulation. This technique is widely used in many different applications when an analytical solution is prohibitive. It is perfectly suited for calculating the EV win probability.

The Election Model uses a 5000 election trial simulation. The win probability is the total number of winning election trials/5000. The average electoral vote is calculated for the 5000 election trials. Of course, the average will only be an approximation to the theoretical value based on the summation formula. But the Law of Large Numbers (LLN) applies: the EV average and median are usually within one or two electoral votes of the theoretical mean. The close match between the Monte Carlo average, median and theoretical (expected) mean electoral vote is proof that 5000 election trials are more than sufficient for the simulation.

Meta-Analysis is an unnecessarily complex method and overkill for calculating the expected Electoral Vote; the EV is calculated by the simple summation formula given above. Princeton Professor Wang projected that Kerry would win 311 electoral votes and a 98% win probability. His model was close to the exit polls. But Wang was wrong to suggest that his forecast was “wrong” because Bush won undecided voters. Not so. Kerry easily won the late undecided vote.