# Win percentage?

September 26, 2008 9:31 AM Subscribe

What does 'win percentage', as displayed on polling site fivethirtyeight.com, mean, and how is it calculated?

That is, it's the percentage of simulated elections that each candidate wins.

posted by mr_roboto at 10:32 AM on September 26, 2008

posted by mr_roboto at 10:32 AM on September 26, 2008

Yeah, one of the nice things about FiveThirtyEight is that they explain their methodology in great detail.

posted by DevilsAdvocate at 10:40 AM on September 26, 2008

posted by DevilsAdvocate at 10:40 AM on September 26, 2008

Here's more from their FAQ:

What is Win % or Win Probability? Simply, the number of times that a candidate wins a given state, or wins the general election, based on 10,000 daily simulation runs.

How is Win Probability determined? By simulating the election 10,000 times each day by means of a Monte Carlo analysis, based on the current Projection in each state. The simulation accounts for the following properties:

(i) That the true margin of error of a poll is much higher than the sampling error, especially when the poll is taken long before the election.

(ii) That polling movement between different states tends to be correlated based on the demographics in those states.

posted by nitsuj at 2:31 PM on September 26, 2008

What is Win % or Win Probability? Simply, the number of times that a candidate wins a given state, or wins the general election, based on 10,000 daily simulation runs.

How is Win Probability determined? By simulating the election 10,000 times each day by means of a Monte Carlo analysis, based on the current Projection in each state. The simulation accounts for the following properties:

(i) That the true margin of error of a poll is much higher than the sampling error, especially when the poll is taken long before the election.

(ii) That polling movement between different states tends to be correlated based on the demographics in those states.

posted by nitsuj at 2:31 PM on September 26, 2008

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"Fourthly, we simulate the election 10,000 times for each site update in order to provide a probabilistic assessment of electoral outcomes based on a historical analysis of polling data since 1952. The simulation further accounts for the fact that similar states are likely to move together, e.g. future polling movement in states like Michigan and Ohio, or North and South Carolina, is likely to be in the same direction."

posted by jaimev at 9:35 AM on September 26, 2008