By Perry Bacon Jr. @ FiveThirtyEight.com, June 26

The defining divide in American politics is probably between Republicans and Democrats. It encapsulates all our other divides — by race, education, religion and more — and it’s growing.

This partisan divide is such a big part of people’s political identities, in fact, that it’s reinforced simply by “negative partisanship,” or loyalty to a party because you don’t like the other party. A Pew Research Center poll from last year found that about 40 percent of both Democrats and Republicans belong to their party because they oppose the other party’s values, rather than because they are particularly aligned with their own party.

But what if Americans’ views of the parties, particularly whichever one they don’t belong to, are, well, kind of wrong? That’s the argument of a study by scholars Douglas Ahler and Gaurav Sood that was recently published in The Journal of Politics. They had the polling firm YouGov ask American adults to estimate the size of groups in each party. For example, what percentage of Democrats are black, or lesbian, gay or bisexual? What percentage of Republicans earn more than $250,000 a year, or are age 65 or older?

What they found was that Americans overall are fairly misinformed about who is in each major party — and that members of each party are even more misinformed about who is in the other party [....]