But aren’t strong partisans the most informed, consuming a lot of media about politics? And shouldn’t all that information, well, inform? Maybe not so much. People who consume news media “most of the time” are almost three times as inaccurate in their understanding of others’ views as those who consume news “only now and then,” the study found. This is almost certainly a function of partisans’ compulsive consumption of media sources that support their existing biases. Your political IQ is probably higher after watching reruns of “Full House” than hour after hour of political TV shows.

Heavy social-media use has the same negative effect on viewpoint accuracy. The perception gap is about 10 percentage points higher for those who have shared political content on social media in the past year than those who haven’t. That isn’t much of a shock. Consider, for example, that only about 22 percent of U.S. adults are on Twitter, and 80 percent of the tweets come from 10 percent of users. If you rely on Twitter for political information, you are being informed by ersatz pundits (and propaganda bots) residing within 2.2 percent of the population.

Politicians — especially presidential candidates these days — make the problem worse. They play to stereotypes by saying (or tweeting) radical things to fire up fringe-view supporters, who are numerically small but powerful in primaries. Or they tell their supporters that the other side is all a bunch of extremist kooks.