Leveraging Peer-to-Peer Networks in Pharmaceutical Marketing - Innovation and Marketing in the Pharmaceutical Industry - page 452

directional in nature leading to a better idea of the influence of these physicians.
Physician X may be a high prescribing physician but he is not connected to many
other physicians whom he can influence (only three other physicians as shown in
Fig. 15.1 ). Physician Y on the other hand is socially central and is very well connected.
Physician Y is in a better position to influence a large number of physicians and be
influenced by them. Physician Z, is neither socially central nor high prescribing, but
she is the key link between two groups of physicians. Physician Z seems to be a node
who is key to access to two large groups of physicians and so may be an important
physician to target by pharmaceutical firms trying to increase their reach.
Freeman ( 1978 ) defines three main measures of “network centrality” which
gives a rough indication of the social power of a node based on how well they
“connect” the network—“Degree,” “Closeness” and “Betweenness.” Measures
based on the degree, the number of points with which a point is directly connected,
indicate the communication activity of a point. In directed networks, centrality in
terms of outdegree and indegree is different. In friendship choice networks the
number of choices received (indegree) generally indicates centrality (popularity);
in influence networks centrality is based on the number of outgoing relationships
(outdegree). Degree - based measures indicate local centrality, as the global structure
of the network is not taken into account. In Fig. 15.1 , physician X has degree 3,
physician Y degree 18, and physician Z degree 4. So, physician Y is more central in
the network since she is connected to more physicians than physician X or Z.
Distance - based measures indicate the relative proximity of points with other points
in the network and the extent to which a point can communicate with other points
independently of others. In this context, the distance from a point to another point is
the minimum number of ties that must be used to transmit a message to that point,
the length of a shortest path. Using Fig. 15.1 , we can calculate that the closeness
between physicians X and Y is 6, while that between physician Z and physicians X
or Y is 3. So, we know that physicians X and Z are more close than physicians X and
Y, and so information will take a longer time to travel from physician X to physician
Y, as compared with physician Z, and in this case will have to go through physician
Z. Betweenness or rush is the third type of centrality and measures how important a
point is for the transmission of information between other points. Betweenness
measures assume that information is mainly transmitted through shortest paths,
connections based on the lowest number of consecutive ties. So, in the example in
Fig. 15.1 , physician Z will have a higher betweenness measure than physicians Y or
Z. A fourth measure suggested by Freeman ( 1978 ) is based on prestige or status.
Status-based measures take all direct and indirect connections into account. They
were originally developed to indicate centrality in influence networks.

15.1.2 Physician Social Networks

Physician social networks are built in several ways. There are three main ways in
which physician networks are formed—by social links, by job and location links,
and by professional links. First, physicians who study together in a medical school