Using data from the social network Facebook, MIT students find that just by looking at a person’s online friends, they could predict whether someone is homosexual.

From the NYT:

… The idea behind the MIT work, done in 2007, is as old as the adage that birds of a feather flock together. For years, sociologists have known of the “homophily principle” – the tendency for similar people to group together. People of one race tend to have spouses, confidants, and friends of the same race, for example. Jernigan and Mistree downloaded data from the Facebook network, choosing as their sample people who had joined the MIT network and were in the classes 2007-2011 or graduate students. They were interested in three things people frequently fill in on their social network profile: their gender, a category called “interested in” that they took to denote sexuality, and their friend links.

Using that information, they “trained” their computer program, analyzing the friend links of 1,544 men who said they were straight, 21 who said they were bisexual, and 33 who said they were gay. Gay men had proportionally more gay friends than straight men, giving the computer program a way to infer a person’s sexuality based on their friends.

Then they did the same analysis on 947 men who did not report their sexuality. Although the researchers had no way to confirm the analysis with scientific rigor, they used their private knowledge of 10 people in the network who were gay but did not declare it on their Facebook page as a simple check. They found all 10 people were predicted to be gay by the program. The analysis seemed to work in identifying gay men, but the same technique was not as successful with bisexual men or women, or lesbians. …