The followup paper to the prior one I summarized here, also published in Science, re-does the Milgram letter experiments over email. Before going further, here is the citation:

 Dodds, P. , Muhamad, R., Watts, D.
 An Experimental Study of Search in Global Social Networks.
 Science Vol 301. 8 August 2003.

They take the letter-writing experiments global, ultimately involving over 60,000 people in 13 countries, all trying to route messages to one of 18 targets with only local information. They found the following bits of interesting information:

  • Friends are routed to far more than other relationship-types
  • Work ties, School ties, and family ties are the three highest sources of the acquaintance, in decreasing order
  • People route to “fairly-close” friends more often than very close friends.

They verify that email, as with letters, reaches its target in 5-7 hops using local-knowledge social routing. And they find that routing in this experiment was fairly egalitarian – that is, no one person was critical to the success of the messages reaching targets. This is an interesting experiment to see how the prior letter-writing one would apply to the digital world. In addition, it collected some useful statistics about the types of people we choose when trying to route information to a target.