Science of Networks
Sarita Yardi
syardi3@gatech.edu
http://www.cc.gatech.edu/~yardi/

Categories

◦ Have one or more properties as an aggregate of individuals
◦ Examples: girl, shoes, basketball players
Groups

◦ Solitary unit
◦ Defined by dense, tight boundaries
◦ Examples: family, workgroup
Networks

◦ Set of individual units connected by some relationship
◦ Examples: friendships, organizations, Internet

Email communication between 436 employees (Adamic and Adar, 2005)
Social Networks

Zachary, 1977
Early Example:
Karate Club

Early Example: Bearman PS, Moody J, Stovel K.
Adolescent Sexual Networks

Accessible

Existing connections

Articulated relationships

Visible relationships

Persistent

Characteristics of Online
Social Networks

Paths
Stars
Cycles
Complete
Graphs
Network Topology

Directionality

Strong Ties

◦ Structurally strong
◦ Meet frequently
◦ Emotional connection
◦ Examples: family, close friends
Weak Ties

◦ Long-range
◦ Relationally weak
◦ Less frequent interaction
◦ Lower trust and influence
◦ Access to new ideas and information
◦ Examples: friends of friends, community members
The Strength of Weak Ties

Email communication between 436 employees (Adamic and Adar, 2005)
Power in Networks

Network Density

Six Degrees

Centrality

Albert and Barabasi (1999)
Random Graphs

Albert and Barabasi (1999)
Power Law

mutual friends  clusters  contagions
How do Communities Grow?

80% of peas are produced by 20% of peapods

80% of the land in Italy is owned by 20% of the population

80% of profits are produced by 20% of the employees

80% of customer service problems are created by 20% of

consumers
80% of decisions are made during 20% of meeting time

80% of crime is committed by 20% of individuals

80% of trophies are won by 20% of clubs in by the Ghana

Football Association
80/20 Rule

Syphilis

Adamic and Glance, 2005
Political Blogs

http://www.orgnet.com/divided.html
Political Books

Friendship network of children in a U. S. school, by James Moody
Children’s Friendships

Erdos Number

A social network of sexual contacts, redrawn from the HIV data of J. J. Potterat et
al, \"Risk network Structure in the early epidemic phase of HIV transmission in
Colorado Springs,\" Sexually Transmitted Infections, 78 (2002). Pp. i159-i163.
Sexual Contacts

http://www.aaronkoblin.com/work/flightpatterns/index.html
Air Traffic Control

Nicholas A. Christakis and James H. Fowler. 2007. The Spread of Obesity in a
Large Social Network. The New England Journal of Medicine
Obesity

Venting to her friends on Facebook one night, a religion professor at
Dartmouth College updated her profile to say that she had just
consulted an online encyclopedia entry on \"modernity\" to prepare for
her class the next day.
\"I feel like such a fraud,\" she wrote on her profile. \"Do you think
dartmouth parents would be upset about paying $40,000 a year for
their children to go here if they knew that certain professors were
looking up stuff on Wikipedia and asking for advice from their
Facebook friends on the night before the lecture?“
Her profile featured other comments as well, including a dig at her
colleagues: \"Some day, when i am chair, we're all going to JOG IN
PLACE throughout the meeting. this should knock out at least half of
the faculty within 10 minutes (especially the blowhards) & then the
meeting can be ended in a timely manner.\"
Case Study

Questions?