Networks can be used to represent friendships, with people represented as nodes and if two people are friends, an edge is drawn between the nodes representing them.

It generally happens that, on average, an individual’s friends have more friends than that individual, a phenomenon referred to as the friendship paradox.

It is an example of how in a network, the structure may distort an individual’s local observations.

This phenomenon has been used, for example, in epidemics to choose to vaccinate people who have a greater probability to have contact with other people.

For example, take a random sample of a thousand people, ask each one to name a friend, and vaccinate the 1,000 friends named by these people.