High School Dating (Bearman, Moody, and Stovel, 2004) (Image by Mark Newman)

Corporate E-Mail Communication (Adamic and Adar, 2005)

A course on how the social, technological, and natural worlds are connected, and how the study of networks sheds light on these connections. Topics include: how opinions, fads, and political movements spread through society; the robustness and fragility of food webs and financial markets; and the technology, economics, and politics of Web information and on-line communities.

The course is designed at the introductory undergraduate level with no formal prerequisites; it satisfies the Arts & Sciences Social and Behavioral Analysis (SBA) distribution and the Engineering Liberal Studies (SBA group) distribution.

Course Staff

• Instructors:
  • David Easley, 434 Uris Hall.
  • Austin Benson, 413B Gates Hall.


• Course Staff:
  • Angel Nugroho (akn35)
  • Brandon Quinlan (bmq4)
  • Cathy Xin (cyx5)
  • David Yu (yy743)
  • Fikri Pitsuwan (fp67)
  • Hannah Marks (hrm55)
  • Jessie Liu (jl2686)
  • Jia Wei (jw984)
  • Jinwen Zhu (jz872)
  • Joshua Levine (jrl345)
  • Kelly Yu (ky356)
  • Noe Abernathy (ana48)
  • Peter Zeiger (pjz27)
  • Renee Mirka (rem379)
  • Rishab Bhandari (rb725)
  • Robyn Bardmesser (rjb379)
  • Seong Hwan Kim (sk2347)
  • Thomas Koconis (tck35)
  • Varun Maheshwari (vm324)
  • Vivian Fan (vcf3)
  • Xiaohan Gao (xg63)

CMS Site

At the CMS site, you can log in with your Cornell NetID to find information about your course grades and also to upload solutions to homework.

Solutions to all problem sets must be typed and submitted through the CMS site. The site will require files to be in PDF format. Also, you should check the CMS site at the start of the semester to make sure that you are able to log in. Please let us know if you experience any difficulties with this.

Class Discussion on Piazza

We will be using Piazza as a discussion forum for the class. Feel free to post any questions you have about class. Only students and instructors in the class will be allowed to post to it, and students and instructors and TAs can all answer questions.

To get started, please add yourself to the class piazza page as a student using your @cornell.edu email address.

Class Blog

We will be maintaining a class weblog as part of the course, and posting to the blog will be part of the graded coursework, as described in the accompanying handout. Information about the mechanics of posting can be found in the opening blog post.

Office Hours

• Mon 5:00 - 6:00pm: Robyn, Rhodes 576
• Tue 1:30 - 2:30pm: Prof. Easley, 227 Gates
• Tue 3:00 - 4:00pm: Jessie and Kelly, Rhodes 576
• Wed 9:00 - 10:00am: Prof. Benson, 413B Gates
• Wed 1:00 - 2:00pm: Hannah and Noe, Rhodes 576
• Wed 4:00 - 5:00pm: Varun and Seong Hwan, Rhodes 576
• Wed 5:00 - 6:00pm: Rishab and Cathy X, Rhodes 576
• Wed 6:00 - 7:00pm: David and Joshua, Rhodes 576
• Thu 1:00 - 2:00pm: Renee and Vivian, Rhodes 576
• Thu 3:00 - 4:00pm: Cathy Z and Angel, Rhodes 576
• Thu 4:00 - 5:00pm: Xiaohan and Fikri, Rhodes 576
• Thu 5:00 - 6:00pm: Brandon and Thomas, Rhodes 576
• Thu 6:00 - 7:00pm: Jia and Peter, Rhodes 576

Materials

• We will be using the book Networks, Crowds, and Markets (Cambridge University Press, 2010), which Professor Easley co-wrote while teaching this course over the past several years. A complete draft is on-line at the Web page for the book, and the hardcopy version is for sale at the Campus Store.
• Over the past several years, we've offered an on-line version of the course through the edX platform. The materials from this course are now archived, and you can access them by registering on-line at the edX site. Although you can no longer take the edX course as a student, by registering you get access to the videos and on-line exercises. In the course this fall, this edX material will serve as a set of optional resources that you may find helpful for alternate presentations as well as a source of additional practice exercises.
• We'll use clickers in lecture. You must use a clicker from the iClicker system. Academic integrity guidelines require that you may only use your own registered clicker during class. The process for registering an iClicker is described in the registration instructions.

Outline of Topics

(1) Graph Theory and Social Networks

The course begins with a discussion of some of the general properties of networks. It develops this through examples from social network analysis, including the famous ``strength of weak ties'' hypothesis in sociology, and it connects these themes to recent large-scale empirical studies of on-line social networks.

Readings

• Chapters 1-3 and Chapter 5.

Optional further reading:

• Mark Granovetter. The strength of weak ties. American Journal of Sociology, 78:1360--1380, 1973.
  (This is Granovetter's original paper describing his work covered in Chapter 3 of the Networks book.)
• Johan Ugander, Brian Karrer, Lars Backstrom, and Cameron Marlow. The Anatomy of the Facebook Social Graph. arXiv, 2011.
• Jure Leskovec, Daniel Huttenlocher, and Jon Kleinberg. Signed Networks in Social Media. Proceedings of the SIGCHI Conference on Human Factors in Computing Systems, 1361--1370, 2010.

(2) Game Theory

Since most network studies require us to consider not only the structure of a network but also the behavior of the agents that inhabit it, a second important set of techniques comes from game theory. This too is introduced in the context of examples, including the design of auctions and some ``paradoxical'' phenomena surrounding network traffic congestion.

Readings

• Chapters 6, 8, and 9. (We will cover Chapter 7 later in the semester.)

Optional further reading:

• Ignacio Palacios-Huerta. Professionals Play Minimax. Review of Economic Studies, 70(2003), pp. 395-415,
  (This is the paper that studies penalty kicks in soccer, as discussed in Section 6.8.)

(3) Markets and Strategic Interaction on Networks

The interactions among participants in a market can naturally be viewed as a phenomenon taking place in a network, and in fact network models provide valuable insights into how an individual's position in the network structure can translate into economic outcomes. This provides a natural illustration of how graph theory and game theory can come together in the development of models for network behavior. Our discussion in this part of the course also builds on a large body of sociological work using human-subject experiments to study negotiation and power in networked settings.

Readings

• Chapters 10-12.

(4) Information Networks and the World-Wide Web

The Internet and the Web of course are central to the argument that computing and information is becoming increasingly networked. Building on the earlier course topics, we describe why it is useful to model the Web as a network, discussing how search engines make use of link information for ranking, how they use ideas related to power and centrality in social networks, and how they have implemented network-based matching markets for sellling advertising.

Readings

• Chapters 13-15.

(5) Network Dynamics: Population Models

Networks are powerful conduits for the flow of information, opinions, beliefs, innovations, and technologies. We begin by considering how these processes operate at the level of populations, when we can't necessarily observe the network itself, but only its effects on aggregate behavior. As part of this, we consider phenomena including information cascades, "tipping points" in the success of products with network effects, and the distribution of popularity.

Readings

• Chapter 7, Chapters 16-18, and Chapter 22.

(6) Network Dynamics: Structural Models

We continue our exploration of how things flow through networks, focusing on what we can learn from details of the network structure itself. Here we study how both behaviors and diseases can spread through a social network, and also some of the network phenomena that underpin the "six degrees of separation" effect.

Readings

• Chapters 19-21.

Optional further reading:

• Lars Backstrom, Paolo Boldi, Marco Rosa, Johan Ugander, and Sebastiano Vigna. Four Degrees of Separation. Proceedings of the fourth ACM International Conference on Web Science (WebSci), 2012.
• Michael Suk-Young Chwe. Structure and Strategy in Collective Action. American Journal of Sociology 105(1999), pp. 127--156.

(7) Institutions and Aggregate Behavior

Finally, a perspective based on networks can provide novel insights into the structure of social institutions, and into basic policy questions in many areas. We illustrate this theme with examples based on markets, voting theory, and property rights.

Readings

• Chapters 23-24.

Prerequisites

Almost no knowledge of specific mathematical content is assumed, other than some basic probability (random variables, expectation, independence, and conditional probability), which we will briefly review when it first arises.

The main goal of the course will be to build mathematical models of the processes that take place in networks. As such, students will be expected to interpret and work with mathematical models as they come up the course; at the same time, students should also think about how to relate these models to phenomena at a qualitative level.

Coursework

• Midterm: Monday, October 7, in class.
• Final exam: Thursday, December 19, at 9:00 AM.
• 9 problem sets. As described above, these must be typed and submitted as PDFs using the CMS site, by the start of class on the days they are due.
• Class blog: There is a class weblog, and each student should make three posts to it as part of the graded coursework, following the details described in the accompanying blog guideines.

• Grades on the homework, blog posts, midterm, and final will be weighted as follows:
  • Homework: 36% [Note: lowest of 9 homework scores will be dropped]
  • Midterm: 20%
  • Final Exam: 35%
  • Blog Posts: 9% (3 x 3%)
  • iClicker participation: 0% (score will be considered for borderline cases)

Academic Integrity

You are expected to maintain the utmost level of academic integrity in the course. Any violation of the code of academic integrity will be penalized severely.

You are allowed to collaborate on the homework to the extent of formulating ideas as a group. However, you must write up the solutions to each problem set completely on your own, and understand what you are writing. You must also list the names of everyone that you discussed the problem set with.

Collaboration is not allowed on the other parts of the coursework.

Finally, plagiarism deserves special mention here. Including text from other sources in written assignments without quoting it and providing a proper citation constitutes plagiarism, and it is a serious form of academic misconduct. This includes cases in which no full sentence has been copied from the original source, but large amounts of text have been closely paraphrased without proper attribution. To get a better sense for what is allowed, it is highly recommended that you consult the guidelines maintained by Cornell on this topic. It is also worth noting that search engines have made plagiarism much easier to detect. This is a very serious issue; instances of plagiarism will very likely result in failing the course.