(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-ApplicationsStructural/dp/0521387078
2
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
7
Strength of Ties or Links
8
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



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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
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One-mode ego network
13
Ego Network Analysis

Ego Network Analysis combine the perspective of network
analysis with the data of mainstream social science

No computer assisted analysis needed
14
Two-mode Complete Network
15
Two-mode Ego Network
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Two-mode Network Transformation
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From Zan Huang et al., 2009
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Network Analysis: Data Modeling and Analysis
18
Network Distance Matrix
19
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
21
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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?
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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)
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