Facebook paired with the University of Milan to approximate the “number of hops,” or degrees of separation, between all pairs of individuals on Facebook. The study found that while 99.6 percent of all pairs of people on Facebook are connected by five degrees of separation (six hops), 92 percent are connected by only four degrees (five hops). According to Facebook, the average distance in 2008 was 5.28 hops.
The study also found that people are much more closely connected to individuals in their own country. (In any single country most people are connected by only three degrees, or four hops.)
Facebook naturally attributes some of this closeness to Facebook itself, as well as social networks in general. “And as Facebook has grown over the years, representing an ever larger fraction of the global population, it has become steadily more connected,” Facebook said in a blog post announcing the study results.
Facebook acknowledges that its study can’t really be compared with Milgram’s, as Milgram’s subjects had “only limited knowledge of the social network,” while Facebook has “a nearly complete representation of the entire thing.” In other words, it’s possible that a Facebook-esque study in the 1960s would have revealed similar numbers, because Facebook is able to estimate the shortest distance between any two people using its data.