been exhibited for obesity, smoking, happiness, depression, loneliness, word-of-mouth advertising, and the spread of ideas among inventors (10-14,31). Analyses of the full network also show that subjects are 29% (95% C.I. 23% to 36%) more likely to abstain if a person they are directly connected to (at one degree of separation) abstains. The size of the effect for people at two degrees of separation (the friend of a friend) is 21% (95% C.I. 16% to 27%) and for people at three degrees of separation (the friend of a friend of a friend) is 5% (95% C.I. 1% to 10%). Again, at four degrees of separation the effect disappears (2%, 95% C.I. –1% to 6%).
