Table 1 . Definition of key network measures .

Characteristic	Measure
Betweenness	Betweenness is a measure that indicates how much a node is located in the path between other actors or how much a node connects with other nodes (52).
Degree Centrality	The degree of centrality represents the number of ties a node has (53). If a node has many ties compared to its actors, this indicates that the node has a central position in the network. Centrality can also characterise the shape of a whole network.
Density	Density is defined as the number of existing ties divided by the number of possible ties.
Distance	Distance measures the number of ties that separate two actors. If two nodes are directly connected, the distance is one. If these two nodes are separated by one node, the distance is two.
Reachability	Reachability defines the degree by which a node can be reached by other nodes. If a certain number is unreachable by some actors, it means that the network is fragmented. Reachability corresponds to the number of steps maximally needed to reach from one node to any other nodes in the network (48).