My colleagues sometimes ask me whether I think their friends are gay or not and I will go through that guy's friends list to determine his sexuality.
Obviously this is not a foolproof way to tell but I think it is pretty accurate. Logically speaking, how many gay friends would a straight guy have? I would say none or at most zero.
Unless that guy happens to work in the creative industry like fashion or hairdressing.
So when I found this article, its findings are not surprising. To cater for someone who doesn't like reading long articles, these are the key paragraphs.
Using data from the social network Facebook, they made a striking discovery: just by looking at a person’s online friends, they could predict whether the person was gay. They did this with a software program that looked at the gender and sexuality of a person’s friends and, using statistical analysis, made a prediction.
The two students had no way of checking all of their predictions, but based on their own knowledge outside the Facebook world, their computer program appeared quite accurate for men, they said. People may be effectively “outing” themselves just by the virtual company they keep.
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.
Of course, this is not an excuse to go "unfriending" all your gay friends. It's just to let you be aware that this it is possible to be outed this way, but still it is pure speculation on their part. There's no way to be sure unless it is from the horse's mouth.