social network analysis course 2010 - 2011

Social Network AnalysisGuillaume ERETEO

Social Networks

A social network is made of actors (people, organizations, group) that are tied by social links.

Sociograms and graphsactors are represented by points (nodes, vertices) and relations by lines (edges, links, arcs)

• explicit and declared relations

• interactions between actors

• affiliation between actors

Social links

colleague

communicate

like

likeweb

undirected networkswell suited for representing network with symmetric relationships such as facebook

directed networkswell suited for representing network with non reciprocal relationships such as Twitter

weighted networks

well suited for representing the intensity of relationships, the number of interactions (e.g. mails), or the number of affiliations (e.g. shared links).

1

0.5

1

2

3

labelled networkswell suited for representing the type of relationships

family

colleague

father

friend

follow

follow

father

Social network analysis

helps understanding and exploiting the key features of social networks in order to manage

their assets, their life cycle and predict their evolution.

What for?

• To control information flow

• To foster communication

• To improve network resilience

• To trust or not

Diameterthe maximum distance between two actors

Density of links indicates the cohesion of the network

community detection

distribution of actors and activities

community membership

• influences the way information is shared• influences the way actors behave

Centrality: strategic positions

degree centrality focuses on the number of relations:reveal local popularity

[Freeman 1979]

Centrality: strategic positions

closeness centrality focuses on the proximity of actors:reveal capacity to communicate

[Freeman 1979]

Centrality: strategic positionsbeetweenness centrality focuses on intermediary actors reveals brokers and privileged actor in the information flow

[Freeman 1979]

"A place for good ideas"[Burt 1992] [Burt 2004]

Centrality: strategic positionseigen vector centrality focuses on the connections of neighboursreveals actors that are well connected

transitivity of relationshipsevaluating social opportunities

Peter Jack

Paul

tendency to bind with similar others

"Birds of a feather flock together"

"interaction produces similarity, while similarity produces interaction"

[Mika 2005]

Preferential attachement

who will increase its popularity?

Balance Theory[Heider 1958]

Critical mass

Many ways of connecting people!

likes

ingredient

typemainDish

Food

subclassOf

type

Who has the best betweeness?this is a matter of semantic

knows in passing

has met

colleague

works With

works With

friend

Metrics are not sufficient enough

knows in passing

has met

colleague

works With

works With

friend

examples of vizualisation and analysis tools

Touchgraph facebook browser

easily vizualize your facebook social network

http://apps.facebook.com/touchgraph

this is mine

Analyze your facebook network

1. Extract it first with netvizz: http://apps.facebook.com/netvizz

2. Open it with my favorite graph visualization tool: Gephi http://www.gephi.org

extract with Netvizz

• choose the information to include

• Save the file

analyze with Gephi

Your network is undirected

select the force layout

detect communities

highlight communities

compute shortest paths of relations

highlight most popular actors

Highlight brokers

print attributes

NODEXL

• Excel 2007 based social network visualization and analysis tool

• Homepage http://nodexl.codeplex.com

• Tutorial http://casci.umd.edu/images/4/46/NodeXL_tutorial_draft.pdf

Quick overview of the tutorial

"One way to begin using NodeXL is to type in your own edge list. For example, you might type the name of people who are friends in each row filling in the Vertex 1 and Vertex 2 columns"

"Click on the Show Graph button (directly above the graph pane) to show the network of friendships"

"To calculate graph metrics first click on the Graph Metric button on the Analysis section of

the NodeXL Ribbon."

"Vertex metrics can be mapped onto visual attributes. The graph legend shows that Degree is mapped to Size

and Betweenness Centrality is mapped to Opacity."

You can now handle your social capital

The social capital is the "resources embedded in one's social networks, resources that can be accessed or mobilized through ties in the networks" [Lin 2008]

http://www.kstoolkit.org/Social+Network+Analysis

nameGuillaume Erétéo

account

guillaume@ereteo.net

mailmentorOf

mentorOf

organizationorganization

manages

contributes

contributes answers

twitter.com/ereteog