Community Structure

What is it?

  • You have different regions within the network that interact more heavily within their regions than they do across the network
  • Classifications / Reasons for Community Structures
  • Mutuality of ties aka cliques


  • Not robust – one missing link can disqualify a clique
  • Not interesting – everybody is connected, no core-periphery and no centrality measures apply


  • n-cliques
  • The maximal distance between any two nodes is a subgroup is designated by n
  • The diameter (the longest path between any two nodes) may be greater than n
  • You can leave nodes out


  • You need to know at least a proportion (p) of the clique


  • Each node within a group is connected to k other nodes in the group
  • This can be too stringent because you can end up leaving out certain nodes
  • Frequency of ties among members
  • Closeness or reachability of subgroup members
  • Relative frequency of ties among subgroup members compared to nonmembers (proportion)
  • Bipartite networks

Why look for community structure?

  • It gives you a clear depiction of a network (company structure, school structures, government structures)
  • It can help you predict future occurrences
  • Regions (groups of nodes) after affected by their region and will not be influenced by non-region specific changes.
  • Ways to partition communities

Hierarchical clustering

  • Some similarity between two nodes is calculated and begin to nest them
  • There’s no way to know 100% that the communities you’ve found are the most optimal


  • For each node you define a community (“in the same community?” - yes or no is answered per node)
  • Clique Percolation
  • Similar to modularity but not as stringent – it allows for nodes to share communities.

Above are notes I’ve taken to keep track of the material covered in the Social Network Analysis course I am taking on Coursera. Notes are derived from week-based video lectures and supplemental information I’ve found online to help clarify certain concepts. If you are taking this course, most of the information below will be found in Week 4 associated material. If you are not taking the course, I hope you find the information below helpful in your search