How do people form political beliefs? When will they change their minds? When will actual facts matter? A recent study, conducted by political scientist Brendan Nyhan of Dartmouth College and two co-authors, offers some clues.

One group of participants was provided with a 2009 news article in which Sarah Palin claimed that the Barack Obama administration's Affordable Care Act created death panels and that these panels included bureaucrats authorized to decide whether seniors were "worthy of health care." A separate group was given the same news story, but with an appended correction saying that "nonpartisan health care experts have concluded that Palin is wrong."

The study's big question: Would the correction have any effect? Would people who saw the correction be less likely to believe that the Affordable Care Act calls for death panels?