The Friendship Paradox states that your friends have more friends than you do.
Despite sounding like (and being called) a paradox, this actually makes sense mathematically, as well as in real life.
Imagine two people you know: one, called Becky, is a complete extrovert who talks to everyone and loves to go to bars and party and is quick to strike conversation with pretty much anyone. The other, let’s call him Jason, is an introvert, and grumpy to boot. He prefers to stay at home and only leaves the house to be with one or two people whom he trusts, with no desire to meet new people.
It stands to reason that Becky will have more friends, and that you are more likely to have met and be friends with Becky. Jason, on the other hand, will have very few friends, but there is a much lower chance that you will ever get to meet him. Therefore you are more likely to know the more popular people.
What makes the Friendship Paradox interesting is its applications in real life. The Economist reports that epidemiologists can use this paradox to detect flu outbreaks earlier. Rather than choosing a random sample of people to detect their health, they will ask a random sample of people for a random sample of their friends. These friends proved to be, on average, more popular, and therefore more in contact with other people. Tellingly, the infection rate among this group of popular friends peeked two weeks earlier than the population as a whole (and the original random sample).
Read the article here.
