(Social) Networks Analysis I

Prof. Dr. Daning Hu Department of Informatics University of Zurich Sep 17th, 2014

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Outline n  Basic Concepts of Networks

n  Two Modes of Social Network Analysis

n  Network Data Modeling and Analysis (For Tutorial)

n  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?

Tie/Link: Relationship or interaction between two nodes.

Node: Any entity in a network

(person, system, group, organization)

Fundamental Concepts in (Social) Network Analysis

n Node, Actor (Social Network)

n Tie, Link

n Dyad and Triad

n Subgroup and Group

Nodes and Actors

n  “Discrete individual, corporate, or collective social units” (Wasserman/Faust 2008:17)

n  Node Example: Products in a purchase newtork n  Actor Examples: people in a group, departments within in a

corporation, public service agency in a city, nation-states in the world system

n  “Node” does not imply that they have intention or the ability to “act”

Ties and Links

n  Actors (nodes) are linked to one another by social ties (links) ¨  Kinship, role-based, cognitive, affective, interactions, affliations

n  Example of direct ties in SNA (Wasserman/Faust 2008:17): ¨  Evaluation of one person by another (expressed friendship, liking, 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)

n  Indirect ties ¨  Association or affiliation (jointly attending a social event, or

belonging to the same social club)

Undirected vs Directed Ties

n Undirected ties - attended meeting with - email daily with

n Directed ties - lent money to

Strength of Ties or Links

Dyad and Triad

n  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”

n  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

Components n  Maximal sets of nodes in which every node can reach every other by

some path. A connected network has just one component.

Was to Traverse the Network

Two Modes of Social Network Analysis

One-mode complete network

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One-mode ego network

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Ego Network Analysis

n  Ego Network Analysis combine the perspective of network analysis with the data of mainstream social science

n  No computer assisted analysis needed

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Two-mode Complete Network

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Two-mode Ego Network

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Two-mode Network Transformation

n  From Zan Huang et al., 2009, Management Science

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Network Analysis: Data Modeling and Analysis

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Network Distance Matrix

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Network Analysis: Major Data Formats

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

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What do we want to find out through network analysis?

n  How to model the topology of large-scale networks? n  What are the organizing principles underlying their

topology? n  How does the topology of a network affect the diffusion of

information, innovation, fads, contagious diseases, and viruses in a network?

n  How do networks evolve?

What differences exist between a social network analysis and a non-network explanation?

n  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

n  social network analysis: à  refers to the set of actors and the ties among them à  views on characteristics of the social units arising out of structural or

relational processes or focuses on properties of the relational system themselves

à  the task is to understand properties of the social (economic or political) structural environment, and

à  how these structural properties influence observed characteristics and associations among characteristics

à  relational ties among actors are primary and attributes of actors are secondary

(Wasserman/Faust 2008: 6-9)