It is defined as the minimal number of actors in a social network that need to be removed to disconnect the group.
It is thus identical to the question of the node connectivity of a given graph in discrete mathematics.
The vertex-cut version of Menger's theorem also proves that the disconnection number is equivalent to a maximally sized group with a network in which every pair of persons has at least this number of separate paths between them.
This wiki site provides numerous examples and a tutorial for use with R. Some illustrative examples are presented in the gallery below: Perceived Cohesion Scale (PCS) is a six item scale that is used to measure structural cohesion in groups.
In 1990, Bollen and Hoyle used the PCS and applied it to a study of large groups which were used to assess the psychometric qualities of their scale.