What explains the large variation in the number of contacts (degree) that different
participants of social networks have: age, randomness, or some unobservable fitness
measure? To answer this question, I extend the model presented in Jackson and Rogers
(2007) to allow individuals to vary in their ability to attract contacts. I estimate the parameters
of the extended model, using a social network of citations among high-energy physics
papers, and find that the extended Jackson–Rogers model can parsimoniously fit the degree …