Predicting the Next President

5/12/2009

Written by

Sheldon Howard Jacobson
Sheldon Howard Jacobson

Want to know who's going to win the presidential election this year? So did Sheldon H. Jacobson, a professor of computer science at the University of Illinois at Urbana Champaign. To answer the question on his and everyone else's mind, Jacobson, along with a group of computer science and political science students, and collaborators at Southern Illinois University-Edwardsville, created election08.cs.uiuc.edu, a sophisticated computer model to predict the outcome of the election.

While most opinion polls touted in the national news provide only estimates of the nationwide popular vote, Jacobson's model instead uses a mathematical model based on state polling data; it then runs the results through a dynamic programming algorithm to determine electoral results.

"The results from the 2000 and 2004 presidential election suggested that it can be difficult to predict the winner of the presidential election based on popular vote," says Jacobson. "In fact, it is possible that the popular vote and the Electoral College vote can lead to significantly different results."

Jacobson's mathematical model employs Bayesian estimators that use available state poll results to determine the probability that each candidate will win each of the states. Presently, he's using Rasmussen, Quinipac, and Survey USA results to arrive at state polling data. These state-by-state probabilities are then used in a dynamic programming algorithm to determine a probability distribution for the number of Electoral College votes that each candidate will win in the 2008 presidential election.

He has reason to believe that his model provides a more realistic method of predicting the results. In 2004, when most other polls showed Kerry with a clear edge, his model consistently showed a Bush victory.

One reason for the accuracy could be Jacobson's method of assigning "safe" states.

"We take into account 'safe' states--states that each candidate is basically guaranteed to win," says Jacobson. "In 2004, once you took into account Bush's 'safe' states, he had a much narrower gap to close to get to 270 electoral votes than Kerry." In Jacobson's model, a safe state is one in which the candidate has an 85% chance or greater of winning the state.

Another interesting feature of Jacobson's model is its treatment of undecided voters.

"Undecided voters can have a significant role on the outcome of the election. In fact, they are likely to be the ultimate deciders of who will win this election," says Jacobson.

The model accounts for five different voting scenarios involving undecided voters, each considered individually. A "Neutral" scenario provides an unbiased handling of undecided voters. "Strong Republican" and "Strong Democratic" scenarios provide two extreme envelopes around which results can be judged and evaluated, while "Mild Republican" and "Mild Democratic" provide more realistic possibilities if late-breaking information surfaces that shift voter preferences.

Computer science students William Kormos, Aukrit Unahalekhaka, and Eric Johnson maintain a website that displays the latest predictions at election08.cs.uiuc.edu. Political science student Andy Keeney also participates in the project.

So what outcome is the model predicting today? In three voting scenarios (Neutral, Mild Republican, and Strong Republican), John McCain is predicted as the winner. Obama is predicted as the winner for Democrat leaning scenarios.

But, Jacobson warns, opinions can change quickly. He plans to update his model many more times before the election season is over.


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This story was published May 12, 2009.