Researchers at Northwestern University in Evanston, Ill., and Britain's University of Essex analyzed poll data from voters, and not surprisingly, backers of a specific candidate expected their man or woman to win no matter how they fared in polling.
"People thought their preferred candidate had a higher chance of winning, in every election, no matter in which state they live, no matter who was running, no matter which political party," said study co-author Charles Manski. "This is one of the strongest empirical regularities I've ever seen."
Preferred candidates were overrated by supporters regardless of gender, race or level of education.
As an example, Manski, a professor of economics and fellow at the Institute for Policy Research at Northwestern, said someone who strongly backs a Democratic candidate over a Republican will give that Democrat a 20 percent to 30 percent greater chance of winning. He calls the psychology the false consensus effect, in which political backers project their preferences onto others.
"It appears that Americans, despite having access to the same publicly available information, nevertheless inhabit disparate perceptual worlds," he said in a release.
The study, published in the current Proceedings of the National Academy of Sciences Journal, used data from an online survey given several thousand adults by the non-profit RAND Corporation during the 2008 presidential and 2010 congressional and gubernatorial election campaigns.