# Predicting the Presidential Election Result, from Dan Grossman

September 6, 2008 |

Can someone give some explanation why Intrade indicates Obama 59% likely to win and McCain 41%, while the polls show them about even?

Are there any other web sites you find useful in predicting the election?

## Alex Forshaw replies:

The polls don't show them as even. Additionally, the most credible polls (Gallup, Rasmussen, ABC/WP) are generally the ones which show Obama with the largest leads.

Real Clear Politics has a summary of some of the major polls.

## Tom Marks and Jason Ruspini add:

There are two methods to predict the election.

The prediction markets such as Intrade and Iowa Election Markets (chart) are probably the best predictor.  As of 10pm EST today Intrade is giving 57% chance for Obama and 43% for McCain. Iowa is also 53 vs 47.

Another way is to look at polls. However, the polls generally cited by news organizations are national polls which on the surface is fundamentally flawed since it is the Electoral College Vote and not the Popular Vote that determines the election result.

What you must do is look at state polls and infer the Electoral Vote implied by these polls.  Fortunately there are some very nice web sites that do the work for you.  They automatically look up the results of the latest polls and apply statistical adjustments (such as weighting polls differently depending on accuracy and timeliness, or performing Monte Carlo simulations to incorporate the inherent inaccuracy of any poll) to come up with their forecast.

The three best Electoral Vote prediction sites based on state polls are:

Vanderbilt U. Economist A. Moro's Forecast

Five Thirty Eight

Reading about the methodologies these sites use can be interesting for those who are statistically oriented.  Most people probably only care about the result.  Currently Prof. Moro gives 314 votes for Obama. Prof. Wang gives him 311 while FiveThirtyEight gives 309 to Obama. (As every schoolboy knows it takes 270 electoral votes to win the election).

In summary, both methods of prediction currently favor Obama. The rough equality shown by some national polls is misleading.

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