Table 2. Examples of quantitative network measures and how they are related to different network characteristics.

     

Characteristic   Measure
Density   Number of links divided by the number of nodes in the network.
Reachability   Diameter, i.e., the number of steps maximally needed to reach from one node to any other node in the network.
Number of components. A component is an independent network within the larger network in which all nodes are directly or indirectly in contact with each other. If a network consists of more than one component, it is considered fragmented; the degree of fragmentation is quantified by measuring the number of components.
Betweenness   A measure that quantifies the degree of betweenness (Freeman 1979), i.e., how much each node contributes to minimizing the distance between nodes in the network (compare with reachability above). This measure can be applied to individual nodes, and can then be used to identify the actors that contribute most to linking the network. The measure can also be applied to the network as a whole to quantify the degree of modularity, i.e., separation into smaller groups or modules.
Centrality   The degree of centrality indicates how many links a node has (Freeman 1979). This measure can be applied to individual nodes or the whole network. A high degree of centrality for an individual node indicates that it has many links compared to other nodes. Centrality for the whole network indicates the tendency in the network for a few actors to have many links, e.g., a wheel-star structure.