I just read this while waiting at the airport for my flight to Jakarta:

“Participants are 52 per cent more likely to be lonely if a person to whom they are directly connected (at one degree of separation) is lonely,” the authors write.

At two degrees of separation, they were 25 per cent more likely to feel lonely. At three degrees it was 15 per cent and at four degrees the effect disappeared. This pattern – what the authors term the “three degrees of influence rule of social contagion” – also appeared in the obesity, smoking and happiness studies.