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Today’s topics

Today’s topics. Strength of Weak Ties Next Topic How does Google rank webpages in search? Acknowledgements James Moody, Alan Kirman , Dejan Vinkovic. F actors influencing diffusion. Network structure ( unweighted ) density degree distribution clustering connected components

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Today’s topics

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  1. Today’s topics Strength of Weak Ties Next Topic How does Google rank webpages in search? Acknowledgements James Moody, Alan Kirman, DejanVinkovic

  2. Factors influencing diffusion • Network structure (unweighted) • density • degree distribution • clustering • connected components • community structure • Strength of ties (weighted) • frequency of communication • strength of influence • Spreading agent • attractiveness and specificity of information

  3. How does strength of a tie influence diffusion? • M. S. Granovetter: The Strength of Weak Ties, AJS, 1973: • Finding a job through a contact that one saw • frequently (2+ times/week) 16.7% • occasionally (more than once a year but < 2x week) 55.6% • rarely 27.8% • But… length of path is short • contact directly works for/is the employer • or is connected directly to employer

  4. Strength of Weak Ties • Why do leads for new jobs come from weak contacts? • What binds communities together? • How do ties afffect access to resources? • What are the social implications?

  5. Strong ties • A strong tie • frequent contact • affinity • many mutual contacts • Less likely to be a bridge (or a local bridge) “forbidden triad”: strong ties are likely to “close” Source: Granovetter, M. (1973). "The Strength of Weak Ties", American Journal of Sociology, Vol. 78, Issue 6, May 1973, pp. 1360-1380.

  6. Triadic Closure

  7. Triadic Closure

  8. Triadic Closure

  9. Strength of ties on facebook

  10. Strength of ties on Facebook • Why are some ties more common than others?

  11. Strength of ties on twitter Study by Wu, Golder & Huberman

  12. Whatindicates cohesion? • Mutuality of ties • everybody in the group knows everybody else • Closeness or reachability of subgroup members • individuals are separated by at most n hops • Frequency of ties • Among members • everybody in the group has links to at least k others • Among subgroup members compared to nonmembers • Why? • Discover communities of practice • Measure isolation of groups • Threshold processes: • I will adopt an innovation if some number of my contacts do • I will vote for a measure if a fraction of my contacts do

  13. Columbia Small World Experiment • Identical protocol to Travers and Milgram, but conducted via the Internet • 60,000 participants from 170 countries attempting to reach 18 different targets • Results • Median “true” chain length 5 < L < 7 • Successful chains disproportionately used • professional ties (34% vs. 13%) • ties originating at work/college • target's work (65% vs. 40%) • weak ties (Granovetter) • . . . and disproportionately avoided • hubs (8% vs. 1%) (+ no evidence of funnels) • family/friendship ties (60% vs. 83%)

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