Friends You Can Count On (Why Your Friends Have More Friends Than You) in the New York Times.
The magic of weighted averages explains why social butterflies contribute disproportionately to the average number of connections in a group - they name, and are named as, connections more frequently.
The practical implications of this are very cool - grabbing particularly social individuals to monitor for infectious disease can tip off public health agencies to epidemics faster than random sampling. (It’s a finding that Robb actually caught swine flu proving, in 2009.)
