Social Network Analysis: A Brief Introduction

Social network analysis [SNA] is the mapping and measuring of relationships and flows between people, groups, organizations, animals, computers or other information/knowledge processing entities. The nodes in the network are the people and groups while the links show relationships or flows between the nodes. SNA provides both a visual and a mathematical analysis of human relationships. Management consultants use this methodology with their business clients and call it Organizational Network Analysis [ONA].

To understand networks and their participants, we evaluate the location of actors in the network. Measuring the network location is finding the centrality of a node. These measures give us insight into the various roles and groupings in a network -- who are the connectors, mavens, leaders, bridges, isolates, where are the clusters and who is in them, who is in the core of the network, and who is on the periphery?

We look at a social network -- the "Kite Network" above -- developed by David Krackhardt, a leading researcher in social networks. Two nodes are connected if they regularly talk to each other, or interact in some way. Andre regularly interacts with Carol, but not with Ike. Therefore Andre and Carol are connected, but there is no link drawn between Andre and Ike. This network effectively shows the distinction between the three most popular individual centrality measures: Degree Centrality, Betweenness Centrality, and Closeness Centrality.

Degree Centrality

Social network researchers measure network activity for a node by using the concept of degrees -- the number of direct connections a node has. In the kite network above, Diane has the most direct connections in the network, making hers the most active node in the network. She is a 'connector' or 'hub' in this network. Common wisdom in personal networks is "the more connections, the better." This is not always so. What really matters is where those connections lead to -- and how they connect the otherwise unconnected! Here Diane has connections only to others in her immediate cluster -- her clique. She connects only those who are already connected to each other.

Betweenness Centrality

While Diane has many direct ties, Heather has few direct connections -- fewer than the average in the network. Yet, in may ways, she has one of the best locations in the network -- she is between two important constituencies. She plays a 'broker' role in the network. The good news is that she plays a powerful role in the network, the bad news is that she is a single point of failure. Without her, Ike and Jane would be cut off from information and knowledge in Diane's cluster. A node with high betweenness has great influence over what flows in the network. As in Real Estate, the "golden rule" of networks is: Location, Location, Location.

Closeness Centrality

Fernando and Garth have fewer connections than Diane, yet the pattern of their direct and indirect ties allow them to access all the nodes in the network more quickly than anyone else. They have the shortest paths to all others -- they are close to everyone else. They are in an excellent position to monitor the information flow in the network -- they have the best visibility into what is happening in the network.

Network Centralization

Individual network centralities provide insight into the individual's location in the network. The relationship between the centralities of all nodes can reveal much about the overall network structure.

A very centralized network is dominated by one or a few very central nodes. If these nodes are removed or damaged, the network quickly fragments into unconnected sub-networks. A highly central node can become a single point of failure. A network centralized around a well connected hub can fail abruptly if that hub is disabled or removed. Hubs are nodes with high degree and betweeness centrality.

A less centralized network has no single points of failure. It is resilient in the face of many intentional attacks or random failures -- many nodes or links can fail while allowing the remaining nodes to still reach each other over other network paths. Networks of low centralization fail gracefully.

Network Reach

Not all network paths are created equal. More and more research shows that the shorter paths in the network are more important. Noah Friedkin, Ron Burt and other researchers have shown that networks have horizons over which we cannot see, nor influence. They propose that the key paths in networks are 1 and 2 steps and on rare occasions, three steps. The "small world" in which we live is not one of "six degrees of separation" but of direct and indirect connections < 3 steps away. Therefore, it is important to know: who is in your network neighborhood? Who are you aware of, and who can you reach?
In the network above, who is the only person that can reach everyone else in two steps or less?

Boundary Spanners

Nodes that connect their group to others usually end up with high network metrics. Boundary spanners such as Fernando, Garth, and Heather are more central in the overall network than their immediate neighbors whose connections are only local, within their immediate cluster. You can be a boundary spanner via your bridging connections to other clusters or via your concurrent membership in overlappping groups.
Boundary spanners are well-positioned to be innovators, since they have access to ideas and information flowing in other clusters. They are in a position to combine different ideas and knowledge, found in various places, into new products and services.

Peripheral Players

Most people would view the nodes on the periphery of a network as not being very important. In fact, Ike and Jane receive very low centrality scores for this network. Since individuals' networks overlap, peripheral nodes are connected to networks that are not currently mapped. Ike and Jane may be contractors or vendors that have their own network outside of the company -- making them very important resources for fresh information not available inside the company!
Recent applications of SNA...
Reveal how hospital-acquired infection[HAI] spread amongst patients and medical staff
Map and weave nationwide volunteer network
Improve the innovation of a group of scientists and researchers in a worldwide organization
Find emergent leaders in fast growing company
Improve leadership and team chemistry for sports franchises
Build a grass roots political campaign
Determine influential journalists and analysts in the IT industry
Unmask the spread of HIV in a prison system
Map executive's personal network based on email flows
Discover the network of Innovators in a regional economy
Analyze book selling patterns to position a new book
Map a group of entrepreneurs in a specific marketspace
Find an organization's go-to people in various knowledge domains
Map interactions amongst blogs on various topics
Reveal key players in an investigative news story
Map national network of professionals involved in a change effort
Improve the functioning of various project teams
Map communities of expertise in various medical fields
Help large organization locate employees in new buildings
Examine a network of farm animals to analyze how disease spreads from one cow to another
Map network of Jazz musicians based on musical styles and CD sales
Discover emergent communities of interest amongst faculty at various universities
Reveal cross-border knowledge flows based on research publications
Expose business ties & financial flows to investigate possible criminal behavior
Uncover network of characters in a fictional work
Analyze managers' networks for succession planning
Discern useful patterns in clickstreams on the WWW
Locate technical experts and the paths to access them in engineering organization