Joe Keohane writes about partisanship and facts in an article in the Boston Globe
In a series of studies in 2005 and 2006, researchers at the University of Michigan found that when misinformed people, particularly political partisans, were exposed to corrected facts in news stories, they rarely changed their minds. In fact, they often became even more strongly set in their beliefs.
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The problem is that sometimes the things they [partisan voters] think they know are objectively, provably false. And in the presence of the correct information, such people react very, very differently than the merely uninformed. Instead of changing their minds to reflect the correct information, they can entrench themselves even deeper.
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In reality, we often base our opinions on our beliefs, which can have an uneasy relationship with facts. And rather than facts driving beliefs, our beliefs can dictate the facts we chose to accept. They can cause us to twist facts so they fit better with our preconceived notions. Worst of all, they can lead us to uncritically accept bad information just because it reinforces our beliefs. This reinforcement makes us more confident we’re right, and even less likely to listen to any new information. And then we vote.