How many Americans are married to someone of another political party? Who are they? Are they old or young?

These are some of the questions two researchers at FiveThirtyEight decided to take on. They published their findings Tuesday. Eitan Hersh, one of the researchers, wrote that the study was inspired by evidence that Democrats and Republicans avoid dating each other, living near each other and encouraging their children to marry someone outside their party. Despite this previous research, the FiveThirtyEight found that perhaps a surprising number of couples married outside their party.

The FiveThirtyEight research focused on registered voters in 30 states. They mainly looked at male-female partners who live at the same address, having the same last name, and are within 15 years of age.

The research showed that 30 percent of married households have a mismatched pair. One third are Democrats married to Republicans, and the others are partisans who married independents.

David Graham wrote for The Atlantic that interparty marriage can help with the political polarization seen in many communities. “There is already a pattern of increasing segregation by neighborhood in the United States, and once couples in one-party weddings move in together, they’re likely to choose a neighborhood with their political fellows — creating an ever-crescendoing feedback cycle of hyperpartisanship,” Graham wrote.

In a New York Times column, Ann Hood, a far left-leaning Democrat, wrote about her marriage to a Republican. “Love can sidetrack person,” Hood wrote. “Still, it did not feel good when I told myself: I love a Republican. It felt, in fact, like I had betrayed someone. Or many people.”

FiveThirtyEight compared interparty marriage to interracial marriage. They used voter registration data in Florida, Louisiana and North Carolina, where voter files list everyone by party affiliation and race. In those three states, 11 percent of married couples are in Democratic-Republican homes. By comparison, 6 percent of married couples in those states are in an interracial home.

The data also found that there is a higher rate of mixed-partisan relationships among younger couples. One reason for this is that younger voters are more likely to register as independent than older voters.

Finally, researchers addressed voter participation. They found that partisans married to like-partisans voted at much higher rates than those married to members of the opposite party. Hersh wrote:

Why is there such a big effect on turnout? From this data alone, it is hard to say for sure. But it is likely a combination of two factors. First, voters who are not particularly interested in voting are probably more willing to be in mixed-partisan relationships. Second, living with an independent or opposite-partisan probably also directly affects one’s behavior.