The Small World experiments

“Stanley Milgram was an American researcher in experimental social psychology at Harvard University in Boston, USA. Beginning in 1967, he began a widely-publicized set of experiments to investigate the so-called "small world problem." This problem was rooted in many of the same observations made decades earlier by Karinthy. That is, Milgram and other researchers of the era were fascinated by the interconnectedness and "social capital" of human networks. While it is unknown how directly Milgram was influenced by Karinthy's work, the similarities between the two authors are remarkable. However, while Karinthy spoke in abstract and fictional terms, Milgram's experiments provided evidence supporting the claim of a "small world." His study results showed that people in the United States seemed to be connected by approximately six friendship links, on average. Although Milgram reportedly never used the term "Six Degrees of Separation," his findings likely contributed to the term's widespread credence. Since these studies were widely publicized, Stanley Milgram is also, like Karinthy, often attributed as the origin of the notion of Six Degrees" (From Wikipedia)