Transcript CH2
(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
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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
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Strength of Ties or Links
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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
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One-mode ego network
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Ego Network Analysis
Ego Network Analysis combine the perspective of network
analysis with the data of mainstream social science
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
From Zan Huang et al., 2009
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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?
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)