# What is the probability that your vote determines the outcome of the
Presidential election?

## Andrew Gelman (Dept. of Statistics, UC Berkeley)

It's typically about 1 in 10 million.
To answer this question, you need a probability model of election
outcomes. We first discuss some obvious but wrong ideas and then
present the right general framework for answering this sort of
question.

Our models for elections are extensions of well known results in
political science. The state-by-state outcome of the Presidential
election can be predicted with fair accuracy using information
available before Labor Day. We briefly discuss the political
implication of this fact and then describe a forecasting method based
on a random components linear regression model. As a side issue, we
also address the question of whether the electoral college is biased
in favor of the Democrats or Republicans.

We also discuss the statistical difficulties in creating the model and
compare to models for Congressional elections. This work is joint
with Gary King, Department of Government, Harvard University.