Social Network Analysis Introduction for Political Scientists

Transcript

1. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Social Network Analysis INTA 6003 October 24, 2013 INTA 6003 Social Network Analysis
2. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Introduction Measuring Relationships Cleaning Sampling What is Social Network Analysis? Social network analysis is the study of social relationships using network theory. In political science, it can be used to analyze and understand: How knowledge flows between individuals Clandestine or covert organizations The political power and influence of individuals INTA 6003 Social Network Analysis
3. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Introduction Measuring Relationships Cleaning Sampling Collecting and Cleaning Social Network Data INTA 6003 Social Network Analysis
4. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Introduction Measuring Relationships Cleaning Sampling Terminology Nodes: actors Ties or edges: relations Isolate: an actor with no connections B B E E A A D D C C INTA 6003 Social Network Analysis
5. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Introduction Measuring Relationships Cleaning Sampling Measuring Relationships INTA 6003 Social Network Analysis
6. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Introduction Measuring Relationships Cleaning Sampling Kinds of Relations Academic department faculty examples: Students in common Serve on same committees Interact outside of the workplace Share areas of expertise Co-author papers How might you measure each of these? INTA 6003 Social Network Analysis
7. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Introduction Measuring Relationships Cleaning Sampling Scales of Measurement Binary: absent (0) vs. present (1) Grouped ordinal: e.g. disliked (-1), neutral (0), liked (1) Interval measures: e.g. counting number of emails or phone calls between two people INTA 6003 Social Network Analysis
8. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Introduction Measuring Relationships Cleaning Sampling Cleaning INTA 6003 Social Network Analysis
9. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Introduction Measuring Relationships Cleaning Sampling Conventional Social Science Data Focuses on actors and attributes Rows are observations Columns are quantitative or qualitative scores on attributes, variables, or measures Name Sex Age Bob Male 32 Carol Female 27 Ted Male 29 Alice Female 28 INTA 6003 Social Network Analysis
10. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Introduction Measuring Relationships Cleaning Sampling Pure Expression of Network Data Focuses on actors and relations Rows and columns are the same set of cases, subjects, or observations Cells describe relationships Who reports liking whom? Choice: Chooser: Bob Carol Ted Alice Bob — 1 1 0 Carol 0 — 1 0 Ted 1 1 — 1 Alice 0 0 1 — INTA 6003 Social Network Analysis
11. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Introduction Measuring Relationships Cleaning Sampling Sampling INTA 6003 Social Network Analysis
12. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Introduction Measuring Relationships Cleaning Sampling Sampling Sampling methods: Full network methods Snowball methods Ego-centric networks INTA 6003 Social Network Analysis
13. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Introduction Measuring Relationships Cleaning Sampling Sampling Full network: Collect information about each actor’s ties with all other actors Advantage: Maximum information Full network data necessary to properly define and measure many of the structural concepts of network analysis Drawback: can be costly and difficult to execute INTA 6003 Social Network Analysis
14. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Introduction Measuring Relationships Cleaning Sampling Sampling Snowball sampling: Begin with a focal set of actors Those actors name some of all of their ties Then ask the newly-named actors for their ties Repeat until no new actors are identified, resources run out, or actors being named are not very relevant Drawback: isolates are not located Drawback: sometimes tricky to know where to start sampling INTA 6003 Social Network Analysis
15. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Introduction Measuring Relationships Cleaning Sampling Ego-centric Networks Begin with a selection of focal nodes (egos) Collect information on the connections among the actors connected to each focal ego Can understand the opportunities and constraints the ego has as a result of how they’re embedded in their networks INTA 6003 Social Network Analysis
16. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Introduction Measuring Relationships Cleaning Sampling Facebook Example—Ego-centric network INTA 6003 Social Network Analysis
17. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources SNA in the Social Sciences Representing Social Relations Using Graphs Representing Social Relations Using Matrices Working with Network Data Gephi Example Visualizing Social Network Data INTA 6003 Social Network Analysis
18. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources SNA in the Social Sciences Representing Social Relations Using Graphs Representing Social Relations Using Matrices Working with Network Data Gephi Example SNA in the Social Sciences INTA 6003 Social Network Analysis
19. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources SNA in the Social Sciences Representing Social Relations Using Graphs Representing Social Relations Using Matrices Working with Network Data Gephi Example Casper INTA 6003 Social Network Analysis
20. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources SNA in the Social Sciences Representing Social Relations Using Graphs Representing Social Relations Using Matrices Working with Network Data Gephi Example Casper How do networks emerge? Analyzes social networks of senior managers of biotechnology firms in San Diego 28 years INTA 6003 Social Network Analysis
21. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources SNA in the Social Sciences Representing Social Relations Using Graphs Representing Social Relations Using Matrices Working with Network Data Gephi Example Casper INTA 6003 Social Network Analysis
22. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources SNA in the Social Sciences Representing Social Relations Using Graphs Representing Social Relations Using Matrices Working with Network Data Gephi Example Casper INTA 6003 Social Network Analysis
23. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources SNA in the Social Sciences Representing Social Relations Using Graphs Representing Social Relations Using Matrices Working with Network Data Gephi Example Casper INTA 6003 Social Network Analysis
24. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources SNA in the Social Sciences Representing Social Relations Using Graphs Representing Social Relations Using Matrices Working with Network Data Gephi Example Casper Conclusion Social networks were initially created by former Hybritech managers that created new companies These companies developed a shared labor market pool Career mobility of managers generated and sustained social networks San Diego social networks are robust INTA 6003 Social Network Analysis
25. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources SNA in the Social Sciences Representing Social Relations Using Graphs Representing Social Relations Using Matrices Working with Network Data Gephi Example Krebs INTA 6003 Social Network Analysis
26. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources SNA in the Social Sciences Representing Social Relations Using Graphs Representing Social Relations Using Matrices Working with Network Data Gephi Example Krebs INTA 6003 Social Network Analysis
27. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources SNA in the Social Sciences Representing Social Relations Using Graphs Representing Social Relations Using Matrices Working with Network Data Gephi Example Krebs INTA 6003 Social Network Analysis
28. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources SNA in the Social Sciences Representing Social Relations Using Graphs Representing Social Relations Using Matrices Working with Network Data Gephi Example Krebs INTA 6003 Social Network Analysis
29. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources SNA in the Social Sciences Representing Social Relations Using Graphs Representing Social Relations Using Matrices Working with Network Data Gephi Example Krebs Findings Covert networks don’t behave like normal social networks — strong ties mostly remain dormant and hidden Hijacker network had a hidden strength — massive redundancy through trusted prior contacts Many of the ties were concentrated around the pilots — risky INTA 6003 Social Network Analysis
30. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources SNA in the Social Sciences Representing Social Relations Using Graphs Representing Social Relations Using Matrices Working with Network Data Gephi Example Questions What might you use SNA for in your research? What sampling method might you use for your research? Why? INTA 6003 Social Network Analysis
31. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources SNA in the Social Sciences Representing Social Relations Using Graphs Representing Social Relations Using Matrices Working with Network Data Gephi Example Representing Social Relations Using Graphs INTA 6003 Social Network Analysis
32. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources SNA in the Social Sciences Representing Social Relations Using Graphs Representing Social Relations Using Matrices Working with Network Data Gephi Example Graphs (Sociograms) Mathematicians call them “graphs”; Sociologists renamed them “sociograms” Points (nodes) represent actors Lines (edges) represent ties or relations INTA 6003 Social Network Analysis
33. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources SNA in the Social Sciences Representing Social Relations Using Graphs Representing Social Relations Using Matrices Working with Network Data Gephi Example Example Graph INTA 6003 Social Network Analysis
34. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources SNA in the Social Sciences Representing Social Relations Using Graphs Representing Social Relations Using Matrices Working with Network Data Gephi Example Types of Graphs Directed graph Simple (undirected) graph B B E E A A D D C C INTA 6003 Social Network Analysis
35. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources SNA in the Social Sciences Representing Social Relations Using Graphs Representing Social Relations Using Matrices Working with Network Data Gephi Example Example Directed Graph https://class.coursera.org/sna-003/class/index INTA 6003 Social Network Analysis
36. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources SNA in the Social Sciences Representing Social Relations Using Graphs Representing Social Relations Using Matrices Working with Network Data Gephi Example Questions What do nodes and edges represent? How are they represented on a graph? Was Casper analyzing directed or undirected graphs? What about Krebs? INTA 6003 Social Network Analysis
37. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources SNA in the Social Sciences Representing Social Relations Using Graphs Representing Social Relations Using Matrices Working with Network Data Gephi Example Representing Social Relations Using Matrices INTA 6003 Social Network Analysis
38. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources SNA in the Social Sciences Representing Social Relations Using Graphs Representing Social Relations Using Matrices Working with Network Data Gephi Example What is a matrix? A matrix is a rectangular arrangement of a set of elements. INTA 6003 Social Network Analysis
39. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources SNA in the Social Sciences Representing Social Relations Using Graphs Representing Social Relations Using Matrices Working with Network Data Gephi Example Adjacency Matrix An adjacency matrix is a square matrix with as many rows and columns as there are actors in the dataset. The values in the cells of the matrix record information about the ties between each pair of actors. INTA 6003 Social Network Analysis
40. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources SNA in the Social Sciences Representing Social Relations Using Graphs Representing Social Relations Using Matrices Working with Network Data Gephi Example Rows: source of directed ties Columns: target of directed ties Bob Carol Ted Alice Bob — 1 1 0 Carol 0 — 1 0 Ted 1 1 — 1 Alice 0 0 1 — INTA 6003 Social Network Analysis
41. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources SNA in the Social Sciences Representing Social Relations Using Graphs Representing Social Relations Using Matrices Working with Network Data Gephi Example Symmetric adjacency matrix A B C D A — 1 0 0 B 1 — 1 0 C 0 1 — 1 D 0 0 1 — Asymmetric adjacency matrix A B C D A — 1 1 1 B 1 — 1 0 C 0 1 — 1 D 0 0 1 — INTA 6003 Social Network Analysis
42. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources SNA in the Social Sciences Representing Social Relations Using Graphs Representing Social Relations Using Matrices Working with Network Data Gephi Example Questions Why is the diagonal blank in adjacency matrices? What kinds of networks are represented by symmetric versus asymmetric matrices? INTA 6003 Social Network Analysis
43. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources SNA in the Social Sciences Representing Social Relations Using Graphs Representing Social Relations Using Matrices Working with Network Data Gephi Example Working with Network Data INTA 6003 Social Network Analysis
44. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources SNA in the Social Sciences Representing Social Relations Using Graphs Representing Social Relations Using Matrices Working with Network Data Gephi Example Manipulating Network Data Structures We typically have attribute data Name Sex Age Board Bob M 42 1 Carol F 44 1 Ted M 39 1 Alice F 27 0 But we want to work with adjacency matrices Bob Carol Ted Alice Bob — 1 1 0 Carol 1 — 1 0 Ted 1 1 — 0 Alice 0 0 0 — INTA 6003 Social Network Analysis
45. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources SNA in the Social Sciences Representing Social Relations Using Graphs Representing Social Relations Using Matrices Working with Network Data Gephi Example Turning Relations into Attributes Fortunately, software can use matrix algebra to convert attribute data into adjacency matrices (or an edge list). UCINET: Data → Attribute R: igraph package INTA 6003 Social Network Analysis
46. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources SNA in the Social Sciences Representing Social Relations Using Graphs Representing Social Relations Using Matrices Working with Network Data Gephi Example Visualize and Analyze Your Own Facebook Network https://persuasionradio.wordpress.com/2010/05/06/ using-netvizz-gephi-to-analyze-a-facebook-network/ https://class.coursera.org/sna-003/assignment/ view?assignment_id=2 INTA 6003 Social Network Analysis
47. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources SNA in the Social Sciences Representing Social Relations Using Graphs Representing Social Relations Using Matrices Working with Network Data Gephi Example Facebook Example Gephi Layout → ForceAtlas 2 Prevent overlap: checked Scaling: 4 Gravity: 25 Partition: Nodes Refresh sex Change colors Apply INTA 6003 Social Network Analysis
48. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Connection and Distance Basic Demographics Centrality Analyzing Social Network Data INTA 6003 Social Network Analysis
49. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Connection and Distance Basic Demographics Centrality Statistics We can use statistics to: Understand the characteristics of a network Compare individuals within a network (Sometimes) compare networks to each other INTA 6003 Social Network Analysis
50. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Connection and Distance Basic Demographics Centrality Introduction The social network perspective emphasizes multiple levels of analysis: Individual level: some actors have lots of connections; others have fewer More connections mean individuals have access to more and more diverse information Highly connected individuals may be more influential and more influenced Structural level: some networks are well-connected or cohesive; others are not Disease and rumors spread more quickly where there are high rates of connection Information does too More connected populations may be able to problem solve or mobilize resources more effectively INTA 6003 Social Network Analysis
51. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Connection and Distance Basic Demographics Centrality Distance Between Actors Some actors may be able to reach most other members of the population with little effort; they tell their friends who tell their friends, and then everyone knows Other actors may tell the same number of friends, but those friends might not be as well connected, and the message may not go far INTA 6003 Social Network Analysis
52. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Connection and Distance Basic Demographics Centrality Basic Demographics INTA 6003 Social Network Analysis
53. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Connection and Distance Basic Demographics Centrality Basic Demographics Network size Actor degree Density Distance Connected components INTA 6003 Social Network Analysis
54. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Connection and Distance Basic Demographics Centrality Network Size It’s easier for students in a small seminar to exchange information than for students in a lecture of 300 to all know each other and exchange information. But large networks have potential for a larger number of relationships. Gephi example: 243 nodes; 2498 edges INTA 6003 Social Network Analysis
55. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Connection and Distance Basic Demographics Centrality Actor degree Degree is simply a count of how many direct relationships an actor has within the network. Degree Out-degree: usually a measure of how influential the actor may be In-degree: actors with high in-degree may be prestigious; they have access to more information, but can also suffer from information overload Gephi example: average degree = 20.56 INTA 6003 Social Network Analysis
56. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Connection and Distance Basic Demographics Centrality Density The proportion of all possible ties that are actually present. May provide insight into the speed of information diffusion and the extent to which actors have high levels of social capital and/or social constraints. Gephi example: 8.5% of all possible ties are present INTA 6003 Social Network Analysis
57. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Connection and Distance Basic Demographics Centrality Distance Distance measures the distance actors are from each other. If two actors are adjacent, the distance between them is 1. Distance is important for understanding how different actors have different constraints and opportunities as a result of their position in the network. Actors who are close to more individuals may be able to exert more power than those who are more distant. Gephi example: Average path length = 3.29* INTA 6003 Social Network Analysis
58. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Connection and Distance Basic Demographics Centrality Connected Components Is the whole population connected, or are there multiple components? If there are multiple components, not all actors are reachable by all others. Gephi example: Connected components = 10; Largest connected component: 217 people INTA 6003 Social Network Analysis
59. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Connection and Distance Basic Demographics Centrality Casper INTA 6003 Social Network Analysis
60. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Connection and Distance Basic Demographics Centrality Centrality INTA 6003 Social Network Analysis
61. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Connection and Distance Basic Demographics Centrality Centrality There are different ways to measure how “central” an actor’s position is within a network: Degree Closeness Betweenness Each of these has its own definition of what it means to be “central”. In each case, actors who are closer to the “center” tend to have more power. INTA 6003 Social Network Analysis
62. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Connection and Distance Basic Demographics Centrality Centrality http://faculty.ucr.edu/~hanneman/nettext/C10_Centrality.html INTA 6003 Social Network Analysis
63. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Connection and Distance Basic Demographics Centrality Degree Actors who have more ties have greater opportunities because they have choices and are less dependent on any specific other actor. INTA 6003 Social Network Analysis
64. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Connection and Distance Basic Demographics Centrality Closeness Actors who are able to reach other actors at shorter path lengths (or who are more reachable by other actors at shorter path lengths) have favored positions. INTA 6003 Social Network Analysis
65. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Connection and Distance Basic Demographics Centrality Betweenness In the star network, if F wants to contact B, they must do so through A. “A” has the capacity to broker contacts among other actors. INTA 6003 Social Network Analysis
66. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Connection and Distance Basic Demographics Centrality Different Notions of Centrality https://class.coursera.org/sna-003/class/index INTA 6003 Social Network Analysis
67. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Connection and Distance Basic Demographics Centrality Krebs INTA 6003 Social Network Analysis
68. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Software Learning Resources INTA 6003 Social Network Analysis
69. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Software Learning Software Data analysis & visualization: Gephi Data cleaning, analysis, & visualization: R (with SNA and iGraph packages) Data cleaning, analysis, & visualization: UCINET & NetDraw Visualization: Guess Modeling: NetLogo INTA 6003 Social Network Analysis
70. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Software Learning Learning Free online textbook Free online course Need help? Email me: mollie@gatech.edu INTA 6003 Social Network Analysis
71. Collecting and Cleaning Social Network Data Visualizing Social Network Data Analyzing Social Network Data Resources Software Learning Visualize and Analyze Your Own Facebook Network https://persuasionradio.wordpress.com/2010/05/06/ using-netvizz-gephi-to-analyze-a-facebook-network/ https://class.coursera.org/sna-003/assignment/ view?assignment_id=2 INTA 6003 Social Network Analysis