The geography of partisan prejudice

Nationwide, if we disregard the smallest counties (which may be hard to pin down statistically, since they have fewer than 100,000 people), the most politically intolerant county in America appears to be Suffolk County, Massachusetts, which includes the city of Boston. In this part of the country, nine out of every 10 couples appear to share the same partisan leaning, according to the voter-file data. Eight out of every 10 neighborhoods are politically homogeneous. This means that people in Boston may have fewer “cross-cutting relationships,” as researchers put it. It is a mostly white, very urban county with a relatively high education level. All these things tend to correlate with partisan prejudice.

We now assume that the other political side is much more extreme than it actually is, as Matthew Levendusky and Malhotra have found. In a 2012 survey, they found that Republicans rate fellow Republicans as more hard-line on taxes, immigration, and trade than they actually are; and Democrats rate Republicans as even further to the right.

These distortions lead us to make worse decisions. Most obviously, politicians refuse to compromise on things like border walls and budgets, even when it hurts the country. But regular people’s judgments get warped too. For example, parents are less likely to vaccinate their children when the other party’s president is in the White House, according to a 2019 working paper by the Stanford Ph.D. candidate Masha Krupenkin. Regardless of who is in power, mutual-fund managers are more likely to invest in funds handled by fellow partisans, a bias that does not lead to better returns.