Wishful Thinking and Social Influence in the 2008 U.S. Presidential Election

This paper analyzes individual probabilistic predictions of state outcomes in the 2008 U.S. presidential election. Employing an original survey of more than 19,000 respondents, ours is the first study of electoral forecasting to incorporate the influence of respondents’ home states. We relate a range of variables to individual accuracy and predictions, as well as to how accuracy improved over time. We find strong support for wishful thinking bias in expectations, as Republicans gave higher probabilities to McCain victories and were worse at overall prediction. This bias was reduced by greater education and numerical sophistication. In addition, we find that respondents living in states with higher vote shares for Obama were more accurate and displayed less wishful thinking bias. We conclude by showing that suitable aggregations of our respondents’ predictions outperformed Intrade (a prediction market) and fivethirtyeight.com (a poll-based forecast) at most points in time.