When studying a social network one interesting question concerns who are its vital links. Who could you remove without much difference to the network compared to who connects everyone together? Vital go-betweens may not be the most important in terms of their own characteristics or achievements but they take on greater importance because of their role in the network. They provide bridges between disparate groups of people.
Each member of the network (each node) can be measured on the bridges they provide between other nodes. This measure of how much the person links others together is called betweenness centrality.
“To measure the betweenness centrality of an actor, let’s call him Frank, in a given network, one identifies the shortest path between any pair of nodes in that network. If Frank is on that path, he receives one point; if he isn’t, he receives zero points. One repeats that procedure for every possible pair of nodes in the network not including Frank, and adds up all his points for his betweenness centrality score.” (Van Den Bulte and Wuyts, 2007, page 21)
Once we have this number we can assess who is on the greatest number of vital paths and who isn’t. Those on more of the vital paths may typically be boundary spanning individuals. In a workplace perhaps they are the accountant who other staff find it easiest to talk to. They are the bridge that holds the network together. These may well be interesting people, perhaps they literally or metaphorically, are able to speak different languages and so connect up those who can’t communicate. These people won’t necessarily have the most connections, or be seen as the most important, but they often make the world a better place.
Read: Christophe Van Den Bulte and Stefan Wuyts 2007, Social Networks and Marketing, MSI (Marketing Science Institute), Cambridge, MA