Social Network Analysis: A Non- Technical Introduction José Luis Molina Universitat Autònoma de Barcelona

Social Networks? Social networks as a metaphor of a complex world. Social networks as social networking platforms. Social networks as a way of empowerment of local actors for improving the current situation. Social networks as a Theory and Methods for studying social and cultural phenomena.

Network Science … An approach to the study of complexity …complexity Massive data about telecommunications, internet, biology, languages, political networks …

A long history... Moreno Sociometry (1934) Graph Theory (e.g. Harary 1963) Manchester School ( ) American Sociology (1976) INSNA & Computers & Interdisciplinariety

Who is working in SNA today...? The International Network for Social Network Analysis (INSNA)

Network data... For making visible relations among entities we have several options: Direct observation. Database of interactions. Asking (people): Name generators.

Sociograms...

... and Matrices AMRVGBEGJSJMMOCRPPGGJLMAFGDE AMG RVT GBB EG JSP JMF MOS CR PP GG JLM MAR FG DES

Sociocentric and egocentric networks … A sociocentric network is the outcome of a tie definition upon a list of nodes. – Normally a Tie Definition refers to an Institutional Setting (kin, workmates, friends, neighbours, cooperation with, report to …). An egonetwork is the subset of ties surrounding a given ego within the sociocentric network. So, sociocentric and egocentric networks refer to a single Institutional Setting.

Personal Networks A Personal Network is the outcome of using one or more Name Generator about Ego’ alters AND a Tie Definition for connecting her alters. If the list of alters is long enough (30 or more on average) all institutional settings in which ego participate will be represented (kin, friends, coworkers …)

Fundamentals … Vargas-Quesada, Benjamín, Moya-Anegón, Félix de (2007). Visualizing the Structure of Science. [pdf]pdf

Actor. In a social network graph, the actor may also be referred to as the node, vertex, or point. The actor does not necessarily have to represent a concrete unit or individual; it may also be a company, institution, or social group. Link. This may also be called a connection or line, and it may be directional ( arc ) or non- directional ( edge ), depending on whether it indicates the orientation – from one actor to another – or does not. Links may or may not be weighted.  Actor  In a social network graph, the actor may also be referred to as the node, vertex, or point. The actor does not necessarily  have to represent a concrete unit or individual; it may also be a company, institution, or social group.  Link  This may also be called a connection or line, and it may be directional or non-directional, depending on whether it indicates the orientation – from  one actor to another – or does not. In the first case, the link is called an the latter case it is non-directional or reciprocal. Links may or may not be weighted.  There is a special type of link, the self-link or loop, which is produced when an actor makes reference to itself.  Adjacent Actors  Actors that can be found in direct relation or connection via a link.  Neighborhood  Set of actors with which a given actor or node is adjacent.  Indirect Connections  Those made between non-adjacent nodes, through intermediary actors. They can also be called indirect links.  Path  This is the sequence of links and actors that connect two non-adjacent actors, without repeating any of them. The length of the path is determined  by the number of links.  Geodesic Distance  It is the shortest path between two nodes or actors of the network, and can also be denominated geodesic length, or simply distance.  Diameter  It is the longest path between two specific nodes or actors.  Isolated Actors  Actors that have no link or relation with any other actor in the network. They may also be called disconnected actors.  Connectivity of a Graph  A graph is said to be connected if there exists a path between each pair of nodes; if not, the graph is said to be disconnected.  Components  This name is given to each one of the subgraphs or subgroups that make up a network.  Bridge  It is a critical element in the connectivity of a graph. If, by eliminating a specific link between two actors, the graph becomes disconnected, or else  increases its number of components, that link is known as a bridge of the network.  Cutoff Point  A node or actor is considered to be the cutoff if, by eliminating that node, and therefore its links as well, the graph is left disconnected.

Adjacent Actors. Actors that can be found in direct relation or connection via a link. Neighborhood. Set of actors with which a given actor or node is adjacent. Path. This is the sequence of links and actors that connect two non-adjacent actors, without repeating any of them.  Actor  In a social network graph, the actor may also be referred to as the node, vertex, or point. The actor does not necessarily  have to represent a concrete unit or individual; it may also be a company, institution, or social group.  Link  This may also be called a connection or line, and it may be directional or non-directional, depending on whether it indicates the orientation – from  one actor to another – or does not. In the first case, the link is called an the latter case it is non-directional or reciprocal. Links may or may not be weighted.  There is a special type of link, the self-link or loop, which is produced when an actor makes reference to itself.  Adjacent Actors  Actors that can be found in direct relation or connection via a link.  Neighborhood  Set of actors with which a given actor or node is adjacent.  Indirect Connections  Those made between non-adjacent nodes, through intermediary actors. They can also be called indirect links.  Path  This is the sequence of links and actors that connect two non-adjacent actors, without repeating any of them. The length of the path is determined  by the number of links.  Geodesic Distance  It is the shortest path between two nodes or actors of the network, and can also be denominated geodesic length, or simply distance.  Diameter  It is the longest path between two specific nodes or actors.  Isolated Actors  Actors that have no link or relation with any other actor in the network. They may also be called disconnected actors.  Connectivity of a Graph  A graph is said to be connected if there exists a path between each pair of nodes; if not, the graph is said to be disconnected.  Components  This name is given to each one of the subgraphs or subgroups that make up a network.  Bridge  It is a critical element in the connectivity of a graph. If, by eliminating a specific link between two actors, the graph becomes disconnected, or else  increases its number of components, that link is known as a bridge of the network.  Cutoff Point  A node or actor is considered to be the cutoff if, by eliminating that node, and therefore its links as well, the graph is left disconnected.

Geodesic Distance. It is the shortest path between two nodes or actors of the network. Diameter. It is on average the shortest path between every two nodes or actors in a network. Isolated Actors. Actors that have no link or relation with any other actor in the network. They may also be called disconnected actors.  Actor  In a social network graph, the actor may also be referred to as the node, vertex, or point. The actor does not necessarily  have to represent a concrete unit or individual; it may also be a company, institution, or social group.  Link  This may also be called a connection or line, and it may be directional or non-directional, depending on whether it indicates the orientation – from  one actor to another – or does not. In the first case, the link is called an the latter case it is non-directional or reciprocal. Links may or may not be weighted.  There is a special type of link, the self-link or loop, which is produced when an actor makes reference to itself.  Adjacent Actors  Actors that can be found in direct relation or connection via a link.  Neighborhood  Set of actors with which a given actor or node is adjacent.  Indirect Connections  Those made between non-adjacent nodes, through intermediary actors. They can also be called indirect links.  Path  This is the sequence of links and actors that connect two non-adjacent actors, without repeating any of them. The length of the path is determined  by the number of links.  Geodesic Distance  It is the shortest path between two nodes or actors of the network, and can also be denominated geodesic length, or simply distance.  Diameter  It is the longest path between two specific nodes or actors.  Isolated Actors  Actors that have no link or relation with any other actor in the network. They may also be called disconnected actors.  Connectivity of a Graph  A graph is said to be connected if there exists a path between each pair of nodes; if not, the graph is said to be disconnected.  Components  This name is given to each one of the subgraphs or subgroups that make up a network.  Bridge  It is a critical element in the connectivity of a graph. If, by eliminating a specific link between two actors, the graph becomes disconnected, or else  increases its number of components, that link is known as a bridge of the network.  Cutoff Point  A node or actor is considered to be the cutoff if, by eliminating that node, and therefore its links as well, the graph is left disconnected.

Components. This name is given to each one of the subgraphs or subgroups that make up a network. Bridge. It is the link that if it is eliminated, the graph becomes disconnected. Cutoff Point. A node or actor is considered to be the cutoff if, by eliminating it, the graph is left disconnected.  Actor  In a social network graph, the actor may also be referred to as the node, vertex, or point. The actor does not necessarily  have to represent a concrete unit or individual; it may also be a company, institution, or social group.  Link  This may also be called a connection or line, and it may be directional or non-directional, depending on whether it indicates the orientation – from  one actor to another – or does not. In the first case, the link is called an the latter case it is non-directional or reciprocal. Links may or may not be weighted.  There is a special type of link, the self-link or loop, which is produced when an actor makes reference to itself.  Adjacent Actors  Actors that can be found in direct relation or connection via a link.  Neighborhood  Set of actors with which a given actor or node is adjacent.  Indirect Connections  Those made between non-adjacent nodes, through intermediary actors. They can also be called indirect links.  Path  This is the sequence of links and actors that connect two non-adjacent actors, without repeating any of them. The length of the path is determined  by the number of links.  Geodesic Distance  It is the shortest path between two nodes or actors of the network, and can also be denominated geodesic length, or simply distance.  Diameter  It is the longest path between two specific nodes or actors.  Isolated Actors  Actors that have no link or relation with any other actor in the network. They may also be called disconnected actors.  Connectivity of a Graph  A graph is said to be connected if there exists a path between each pair of nodes; if not, the graph is said to be disconnected.  Components  This name is given to each one of the subgraphs or subgroups that make up a network.  Bridge  It is a critical element in the connectivity of a graph. If, by eliminating a specific link between two actors, the graph becomes disconnected, or else  increases its number of components, that link is known as a bridge of the network.  Cutoff Point  A node or actor is considered to be the cutoff if, by eliminating that node, and therefore its links as well, the graph is left disconnected.

Current Applications... Scientits networks, scienciometry … Organizations Internet Social Support Discourse Analysis Data-mining...

A “Perfect” Network... “Edges” = undirected lines. Degree: A = 4 B, C, D, y E = 1

Degree... “Arcs”= directed lines. Indegree of A=0 B,C,D,E = 1. Conversely, the outdegree is: A= 4 B, C, D y E = 0

Matrix

Betweeness... The betweeness counts the times that a node occurs in the geodesics of the network (that is, in the shorter paths between each pair of nodes). A=12 A = 0

Betweeness... A= 0 (there is not a path that occurs through it), as D and C. B= 1 E= 1

Closeness... Closeness measures the capacity of a node to reach the rest of the nodes of the network. For computing this measure is necessary to summarize all the geodesics of each node with the rest of nodes of the network. This measure is the farness. If we compute the reciprocal we can obtain the closeness.

Closeness... (ii) For doing this calculations is necesary to convert first the oriented data in reciprocal data: Farness of A = 6 (A  B:1; A  C:2;A  E:1;A  D:2) Farness of B = 7 (B  A:1; B  C:1;B  E:2;B  D:3) Farness of C = 10 (C  B:1; C  A:2;C  E:3;C  D:4) Farness of E= 7 Farness of D= 10 All geodesics = 40 The closeness of A= 40/6= 6,667 or 66,67%. B= 40/7= 5,714 = 57,14% C= 40/10 = 4 = 40%

Centrality...

Clustering...

Present & Future... Evolution of Networks Community Studies …... It is up to us