DCS/CSCI 2350: Social & Economic Networks Are all the links in - PDF document

10/8/20 DCS/CSCI 2350: Social & Economic Networks Are all the links in a network the same? What is the effect of different types of links? “The strength of weak ties” edges Reading: Ch 3 of Easley-Kleinberg Mohammad T . Irfan 1 The strength of weak ties u Agenda u Connect local/interpersonal properties to global/structural properties u Mathematically prove this local to global link u Show that the “critical” ties are actually weak ties 3 1

10/8/20 Granovetter’s study (1960s) u Acquaintances, not friends, hold critical information about job opportunities 4 Triadic closure B and C are very likely to become friends (Rapoport, 1953) B C A 5 2

10/8/20 Triadic closure 6 Triadic closure u Triadic closure increases clustering coeff. (why?) u Reasons why triadic closure happens Opportunity for B and C to meet 1. B and C can trust each other 2. A wants to reduce stress by making B and C 3. friends u Teen suicide <--> low (local) clustering coefficient (Bearman and Moody, 2004) 7 3

10/8/20 Local bridge F G u An edge whose endpoints do not have any common friend ó An edge which is not a side of B A E any triangle ó An edge whose deletion causes the distance between H I its endpoints to be > 2 C D Q1. Are local bridges important? Why? Local bridges have global implications. Next: under some condition , every local bridge must be a “weak” tie 8 Background for proving local bridges are weak ties u Tie-strength (simplifying gradation, temporal effect, etc.) u Weak (acquaintance) Edge-level property u Strong (friend) u Strong Triadic Closure Property (STCP) Node-level property (Granovetter, 1973) Definition. 9 4

10/8/20 The strength of weak ties u If a node A satisfies STCP and has at least 2 strong ties, then any local bridge it's involved in must be a weak tie. u Proof. 10 Large-scale social networks (real-world) and the strength of weak ties 11 5

10/8/20 Weak ties in Facebook (Marlow et al., 2009) Colleagues High school friends 12 Weak ties in Facebook (cont...) 13 6

10/8/20 Weak ties (passive network) – What’s the use? 14 Twitter (Huberman et al., 2009) 15 7

10/8/20 Are weak ties really powerful? Gladwell: “weak ties seldom lead to high-risk activism” 17 Counter-argument 18 8

10/8/20 Counter-argument 19 Counter-argument 20 9