Today’s topics
Strength of Weak Ties
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Acknowledgements
James Moody, Alan Kirman, Dejan Vinkovic
The Science of Networks
3.1
Factors influencing diffusion
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Network structure (unweighted)
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Strength of ties (weighted)
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density
degree distribution
clustering
connected components
community structure
frequency of communication
strength of influence
Spreading agent
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attractiveness and specificity of information
The Science of Networks
3.2
How does strength of a tie
influence diffusion?
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M. S. Granovetter: The Strength of Weak Ties, AJS, 1973:
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Finding a job through a contact that one saw
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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
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contact directly works for/is the employer
or is connected directly to employer
The Science of Networks
3.3
Strength of Weak Ties
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Why do leads for new jobs come from weak
contacts?
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What binds communities together?
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How do ties afffect access to resources?
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What are the social implications?
The Science of Networks
3.4
Strong ties
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A strong tie
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frequent contact
affinity
many mutual contacts
“forbidden triad”:
strong ties are
likely to “close”
Less likely to be a bridge (or a local bridge)
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
3.5
Triadic Closure
The Science of Networks
3.6
Triadic Closure
The Science of Networks
3.7
Triadic Closure
The Science of Networks
3.8
Strength of ties on facebook
The Science of Networks
3.9
Strength of ties on Facebook
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Why are some ties more common than others?
The Science of Networks
3.10
Strength of ties on twitter
Study by Wu, Golder & Huberman
The Science of Networks
3.11
What indicates cohesion?
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Mutuality of ties
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Closeness or reachability of subgroup members
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everybody in the group knows everybody else
individuals are separated by at most n hops
Frequency of ties
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Among members
• everybody in the group has links to at least k others
• Among subgroup members compared to nonmembers
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Why?
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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
3.12
Columbia Small World Experiment
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Identical protocol to Travers and Milgram, but
conducted via the Internet
60,000 participants from 170 countries attempting to
reach 18 different targets
Results
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Median “true” chain length 5 < L < 7
Successful chains disproportionately used
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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%)
The Science of Networks
3.13