Assortativity is not structural, meaning that it is not a consequence of the degree distribution, but it is generated by some process that governs the network’s evolution.
He analyzed the collaboration networks through several large databases in the fields of biology and medicine, physics and computer science in a five-year window (1995-1999).
The results showed that these networks form small worlds, in which randomly chosen pairs of scientists are typically separated by only a short path of intermediate acquaintances.
The results obtained indicated that the network is scale-free and that its evolution is governed by preferential attachment.
Furthermore, the study showed that the node separation decreases over time, however this trend is believed to be offered by incomplete database and it can be opposite in the full system.