Although issues related to racial identity have progressed to the point where the US is willing to elect a black president twice, its citizens still tend to keep their personal relationships segregated. When it comes to the people we spend time with, "Americans’ preference for same-race alters exceeds their preference for similarity based on any other characteristic," according to a new study of interracial dating.

Using massive amounts of data from the dating site OkCupid, UC San Diego's Kevin Lewis looked at how this self segregation plays out in the online world. Among all of the ethnic groups he examined, there's a strong tendency for people to send messages to other users who belong to the same ethnic group. But people who are willing to go against that trend are typically rewarded—recipients of those messages are more likely to respond to them. And for a short time afterward, they're more likely to initiate contacts across racial boundaries.

According to Lewis, OkCupid is structured in a way to make this sort of analysis valuable. Unlike many other dating sites, which claim to be able to discern users' compatibility via personality profiles, OkCupid lets anyone find anyone else's profile. Results can be filtered based on a set of characteristics, but they're characteristics the users set themselves, not something determined by an algorithm. As a result, the site makes it much easier for people to find and contact just about anyone else in the service.

Lewis did apply some filtering himself, limiting the study to people who were straight and looking to date. Even with those limits, the study was able to track over 125,000 users over a two-and-a-half-month period. Based on the information the users provided, Lewis was able to track Asians, blacks, Indians, Hispanics, and whites and follow their interactions within the service (most other identifying information was removed to maintain anonymity).

At first glance, the OkCupid data seemed to confirm what we already knew. Lewis focused on the initial contact between users—the first message between them, which can either be ignored or set off a larger correspondence that can eventually lead to a date. As in the real world, men end up sending the vast majority of the initial messages, and they generally send them to people of their own ethnicity. "Men and women from all racial backgrounds disproportionately initiate contact with other site users from the same racial background," Lewis concludes.

But the situation changes when he followed up on these initial messages and looked at the replies. The relative favoritism for someone of the same race shrinks dramatically and, in some cases, goes away entirely. For some groups, initial messages were more likely to get a response if they came from someone belonging to a different group entirely (this was true for the Asian, Indian, and Hispanic users).

Over the course of the study, 48,000 users were the recipients of messages from someone outside their racial group. Lewis then tracked the users' behavior over the weeks following that message and found that it briefly changed their behavior. For a few weeks afterward, these users were 37 percent more likely to initiate contact with someone outside their own group. Thus, simply getting a message from outside your ethnicity seems to open your thought process to other possibilities, at least for a little while.

Why does this effect go away? Lewis speculates that the rate of interracial contacts remains so low that the first message will probably end up being swamped by a sea of messages from people of the same ethnicity. Over time, that message of conformity may subconsciously influence people's thinking about who they want to contact.

There are some limitations to this study. For example, to keep the prospects of contact between users geographically realistic, Lewis limited some of the work to users who have ZIP codes that share the first two digits. That assumes that it would be inconvenient for someone in Manhattan to date someone in Brooklyn, which many people don't consider much of a problem. The OkCupid user population might also not be very reflective of the US as a whole.

Still, the sheer number of users gives this study a statistical power that would be hard to match any other way. And given the statistics that show that an increasing number of relationships begin online, the behavior in this digital environment probably has a large and growing influence on real-world social dynamics.

PNAS, 2013. DOI: 10.1073/pnas.1308501110 (About DOIs).