The Science of Networks 3.1 Today’s topics Strength of Weak Ties Next Topic How does Google rank webpages in search? Acknowledgements James Moody, Alan Kirman, Dejan Vinkovic
Feb 24, 2016
The Science of Networks 3.1
Today’s topicsStrength of Weak Ties
Next TopicHow does Google rank webpages in search?
AcknowledgementsJames Moody, Alan Kirman, Dejan Vinkovic
The Science of Networks 3.2
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
The Science of Networks 3.3
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
The Science of Networks 3.4
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?
The Science of Networks 3.5
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.
The Science of Networks 3.6
Triadic Closure
The Science of Networks 3.7
Triadic Closure
The Science of Networks 3.8
Triadic Closure
The Science of Networks 3.9
Strength of ties on facebook
The Science of Networks 3.10
Strength of ties on Facebook Why are some ties more common than
others?
The Science of Networks 3.11
Strength of ties on twitterStudy by Wu, Golder & Huberman
The Science of Networks 3.12
What indicates 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
The Science of Networks 3.13
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%)