Key Players

In this chapter, we provide an overview on the literature on key players in networks. We first introduce the theoretical concept of the key player, which is the agent that should be targeted by the planner so that, once removed, she will generate the highest level of reduction in total activity. We also consider another notion of key player where the planner is targeting a set of network nodes that are optimally positioned to quickly diffuse information, attitudes, behaviors or goods. We then examine the empirical tests of the key-player policies for criminal networks, education, R&D networks, financial networks and diffusion of microfinance. We show that implementing such a policy outperforms other standard policies such as targeting the most active agents in a network.