cvs 886 social economic and information networks
TRANSCRIPT
What?
• Representation of (mainly pairwise) connections
Zachary’s Karate Club
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Why?
• ICT enables connectedness • Lot of Big Data patterns are in networks• Allows the study of
– Hidden communities and connections– Economic interactions– Hubs of information– Scale effects of deployment– Diffusion of behavior– Patterns of formation
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Early Application in Sociology
Eventual Split of Zachary’s Karate Club
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Business Tripod
OB
Econ
Business
OR/CS5
Class themes
Social
Economic
Networks
Info6
Text
• “Networks, Crowds and Markets” by Easley and Kleinberg (Cambridge, 2010)
• Final pre-publication draft is onlinewww.cs.cornell.edu/home/kleinber/networks-book/
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Schedule
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Cross, Borgatti & Parker (2002)
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Evolution of Alliances
Evolution of alliances in Europe leading to WW1(Antal, Krapivsky, Redner, Physica D 2006)
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Global Trade Network 1994
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Online Advertising Networks
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Bibliometric Networks
• http://users.dimi.uniud.it/~massimo.franceschet/networks/nexus/bibliometrics.html13
Network of Abortion Decisions
Fowler & Jeon, Social Networks 30 (2008) 14
Myspace vs Facebook
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Internet Adoption Dynamics
http://www.ictaf.tau.ac.il/e-living.pdf16
TB outbreak
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Product Recommendations
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Spread of obesity from Framingham study
Scale-free networks
Caldarelli, SIAM News (2004)19
Grades
Homeworks (3)Inquizitiv ExerciseExam
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Work
• Homework 3 in total– One homework for every three days of class
• Inquizitiv Work– Crowd-sourced quiz questions on the day’s topic
• Final Exam– Two hour exam at least one week after class ends
(exact time to be finalized)
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Learning Cycles: re-using artifacts
InstructorStudents
(2) Answer
(3) Improve
(1) Create
(4)
• Machine Learning techniques surface most important issues for faculty to verify
• This "seed" faculty interaction then propagates throughout the system
https://www.youtube.com/watch?v=2pN1Nx7-sd0
Current Prototype Design
1. Creation
Students createseveral MCQs
Students answer MCQs and make improvements
2. Answer & Improve 3. Answer & Select
Students vote on bestimprovements and select
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Top Creators Top Improvers
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4. Instructor seed interaction
Instructor answers hard-to-evaluate MCQs surfaced by system and chooses improvements
Student leaderboard
System dynamically determines best contributors and participation
Downsides of MCQs (Multiple-Choice Questions)
Limitations of using MCQs only for testing purposes: • MCQs are ineffective for measuring certain types of problem
solving and the ability to organize and express ideas• A different process is involved in proposing a solution versus
selecting a solution from a set of alternatives; and • Sometimes a MCQ may have more than one defensible “correct”
answer
Sources:• S. J. Burton, R. R. Sudweeks, P. F. Merrill, and B. Wood. "How to prepare better multiple-choice test items: guidelines for university faculty", 1991.
• R. B. Frary. More multiple-choice item writing do’s and don’ts. Practical Assessment, Research & Evaluation, 4(11), 1995• T. M. Haladyna, S. M. Downing, and M. C. Rodriguez. A review of multiple-choice item-writing guidelines for classroom assessment. Applied Measurement in
education, 15(3):309–334, 2002. • J. Kehoe. Writing multiple-choice test items. Practical Assessment, Research & Evaluation, 4(9), 1995.
• D. M. Zimmaro. Writing good multiple-choice exams. Center for Teaching and Learning. University of Texas., 2010.
Value of Posing Questions
• "... question generation is a fundamental component in cognitive processes that operate at deep conceptual levels, such as the comprehension of text and social action (Collins, Brown, & Larkin, 1980; Hilton, 1990; Olson, Duffy, & Mack, 1985), the learning of complex material (Collins, 1985; Miyake & Norman, 1979: Palincsar & Brown, 1984; Schank, 1986), problem solving(Reisbeck, 1988), and creativity (Sternberg, 1987). There also is empirical evidence that improvements in the comprehension, learning, and memory of technical material can be achieved by training students to ask good questions (Davey & McBride, 1986; Gavelek & Raphael, 1985; King, 1989, 1990; Palincsar & Brown, 1984; Singer & Donlan, 1982)."
Source: A. C. Graesser and N. K. Person. Question asking during tutoring. American Educational Research Journal, 31(1):pp. 104–137, 1994.
MCQ exercises
Basics: Terminology
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Graph of my Facebook friends
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Connected graph, component
Two nodes are connected if there is a path (of edges/arcs) from one to the other
A set of nodes that are connected to each other form a connected component
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Facebook graph: Giant component
Randomly formed networks usually have one large component with a large fraction of nodes.
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Key Idea: If there were two large components, even with very little chance of a connection across any individual pair, there is an overwhelming chance there is some connection across them
Why giant component?
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Distance
• How close are two nodes?• Measure minimum number of hops to reach
one from the other
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Distance between two nodes
• Minimum number of edges in a path between them
• Shortest way to reach one from the other
• Simple labeling procedure to compute– Start with one end with label 0 (distance to itself)– Identify all neighbors of labeled nodes and label
them with one higher– Continue until all nodes labeled
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Compute distances from MIT
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Alternate view
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Compute Distances from A
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Compute distances from K
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Practice Problem
• Diameter: maximum distance between any pair of nodes in the graph
• Average Distance: average distance over all pairs of nodes in the graph
Consider 5 nodes, A, B, C, D, E -- how should they be connected such that the average distance equals the diameter exactly?
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Practice
• Diameter: maximum distance between any pair of nodes in the graph
• Average Distance: average distance over all pairs of nodes in the graph
Describe how you could construct a graph in which the diameter is approximately 3 times the average distance. (You can use a large number of nodes to construct such a graph.)
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Solution
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Which is the most central node?
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Closeness versus Betweenness Centrality
• Closeness centrality= 1/(Sum of distances to everybody else)
• Betweenness centrality= Fraction of shortest paths between other pairs that go through the node
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Three notions of centrality
55http://www.orgnet.com/sna.html
Closure (Chapter 3)
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Granovetter’s puzzle
• Interviewed many people with new jobs about how they found job
• Predominant answer: personal contact
• Puzzle: Such contacts were acquaintances rather than close friends
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Triadic Closure
• If you and I have a friend in common, we are more likely (than otherwise) to become friends (e.g., People you may know… in Facebook)
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Why Triadic Closure?
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Bridge
• An edge whose removal puts both sides in different connected components
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Local Bridge
• An edge between two nodes who have no neighbors in common
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Strength of ties
• Weak (w) and Strong (s)
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Strong Triadic Closure
• Do these graphs obey strong triadic closure? If not, why not?
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Find the missing label under STC
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Find a plausible labeling under STC
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STC and Local bridges
• If a node’s ties obey STC and it has at least two strong ties, then all its local bridges must be weak
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Suppose local bridge is a strong tie
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Granovetter’s Puzzle Resolved
• Strong Triadic Closure holds in most nodes in social networks
• Local bridges span across communities and are likely to provide new leads in job searches
• Under these circumstances, these local bridge links (job generating leads) will be weak ties (acquaintances)
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