[JohnKemeny]

I agree that it's difficult, I don't know much about centrality measures for dynamic networks.

However, degree sounds like a bad measure, since the value can be drastically increased by participating in a (few) big project(s).

[mikk14]

All correct, it was also one point raised by the reviewers. They had some suggestions about temporal centrality, but in the end I didn't followup on that because this centrality analysis was just a descriptive part that didn't really support any of the primary nor secondary claims in the paper.