(Social) Networks Analysis I Prof. Dr. Daning Hu Department of Informatics University of Zurich Oct 1st, 2012

Outline Basic Concepts of Networks Two Modes of Social Network Analysis Network Data Modeling and Analysis (For Tutorial) Ref Book: Social Network Analysis: Methods and Applications (Structural Analysis in the Social Sciences) http://www.amazon.com/Social-Network-Analysis-Applications-Structural/dp/0521387078

What is a Network? Node: Any entity in a network (person, system, group, organization) Tie/Link: Relationship or interaction between two nodes.

Fundamental Concepts in (Social) Network Analysis Node, Actor (Social Network) Tie, Link Dyad and Triad Subgroup and Group

Node and Actor “Discrete individual, corporate, or collective social units” (Wasserman/Faust 2008:17) Node Example: Products in a purchase newtork, Computers in the Internet. Actor Examples: people in a group, departments within in a corporation, public service agency in a city, nation-states in the world system “Node” does not imply that they have intention or the ability to “act”

Tie and Link Actors (nodes) are linked to another by social ties (links) Example of direct ties in SNA (Wasserman/Faust 2008:17): Evaluation of one person by another (expressed friendship, linking, or respect) Transfers of material resources (business transactions, lending or borrowing things) Behavioral interaction (talking together, sending messages) Physical connection (a road, river, or bridge connecting two points) Biological relationships (kinship or descent) Indirect ties Association or affiliation (jointly attending a social event, or belonging to the same social club)

Undirected vs Directed Ties

Strength of Ties or Links

Dyad and Triad Dyad: a tie between two actors “consists of a pair of actors and the (possible) tie(s) between them” (Wasserman/Faust 2008:18) Shows “properties of pairwise relationships, such as whether ties are reciprocated or not, or whether specific types of multiple relationships tend to occur together” Triad: “Triples of actors and associated ties” (Wasserman/Faust 2008:19) “a subset of three actors and the (possible) tie(s) among them” (Wasserman/Faust 2008:19) Triadic analyses focus on the fact whether the triad is Transitive : if actor i “likes” actor j, and actor j in turn “likes” actor k, then actor i will also “like” actor k Balanced: if actors i and j like each other, then i and j should be similar in their evaluation of a third actor, k, and i and j dislike each other, then they should differ in their evaluation of third actor, k

Group and Subgroup Group “is the collection of all actors on which ties are to be measured” (Wasserman/Faust 2008:19) Subgroup of actors is defined “as any subset of actors, and all ties among them” (Wasserman/Faust 2008:19) Actors in a group “belong together in a more or less bounded set (…) consists of a finite set of individuals on which network measurements are made” (Wasserman/Faust 2008:19) “however, in research applications we are usually forced to look at finite collections of actors and ties between them.” (Wasserman/Faust 2008:20)

Two Modes of Social Network Analysis

One-mode complete network

One-mode ego network

Ego Network Analysis Ego Network Analysis combine the perspective of network analysis with the data of mainstream social science No computer assisted analysis needed

Two-mode Complete Network

Two-mode Ego Network

Two-mode Network Transformation From Zan Huang et al., 2009

Network Analysis: Data Modeling and Analysis

Network Distance Matrix

Network Analysis: Major Data Formats

Example of Real-World Networks Protein network Freshwater food web The Internet The World-Wide Web High school friendship network

What do we want to find out through network analysis? How to model the topology of large-scale networks? What are the organizing principles underlying their topology? How does the topology of a network affect the diffusion of information, innovation, fads, contagious diseases, and viruses in a network? How do networks evolve?

What differences exist between a social network analysis and a non-network explanation? In non-network explanations the main focus is on: attributes of autonomous individual units, the associations among these attributes, and the usefulness of one or more attributes for predicting the level of another attribute social network analysis: refers to the set of actors and the ties among them views on characteristics of the social units arising out of structural or relational processes or focuses on properties of the relational system themselves the task is to understand properties of the social (economic or political) structural environment, and how these structural properties influence observed characteristics and associations among characteristics relational ties among actors are primary and attributes of actors are secondary (Wasserman/Faust 2008: 6-9)