Who is the Key Player? A Network Analysis of Juvenile Delinquency
提出一种实证方法，识别网络中的关键人物（移除后能最大程度降低整体犯罪活动水平），并利用美国青少年友谊网络数据，发现关键人物并非最活跃的犯罪者，针对关键人物的政策比移除最活跃者更能减少犯罪。
This article presents a methodology for empirically identifying the key player, whose removal from the network leads to the optimal change in aggregate activity level in equilibrium [Ballester, C., Calvó-Armengol, A., and Zenou, Y. (2006), “Who’s Who in Networks. Wanted: The Key Player,” <i>Econometrica</i>, 74: 1403–1417], allowing the network links to rewire after the removal of the key player. First, we propose an IV-based estimation strategy for the social-interaction effect, which is needed to determine the equilibrium activity level of a network, taking into account the potential network endogeneity. Next, to simulate the network evolution process after the removal of the key player, we adopt the general network formation model in Mele [(2017), “A Structural Model of Dense Network Formation,” <i>Econometrica</i>, 85: 825–850] and extend it to incorporate the unobserved individual heterogeneity in link formation decisions. We illustrate the methodology by providing the key player rankings in juvenile delinquency using information on friendship networks among U.S. teenagers. We find that the key player is not necessarily the most active delinquent or the delinquent who ranks the highest in standard (not microfounded) centrality measures. We also find that, compared to a policy that removes the most active delinquent from the network, a key-player-targeted policy leads to a much higher delinquency reduction.