So what happens when you kill or capture the leadership of a terrorist organization? Matthew Dickinson, a graduate student in political science at Duke, decided to find out. H looked at “eight well-known terrorist groups that have survived multiple leadership transitions”: Basque Homeland and Freedom, Hamas, Hezbollah, Irish Republican Army, Palestine Liberation Organization, Popular Front for the Liberation of Palestine, Red Brigades and Sendero Luminoso. The answer?

This study finds that leadership transition generally causes a noticeable and statistically significant increase in attacks and casualties for the months immediately afterward.

Well, that’s comforting. On the bright side, the effect is somewhat stronger when you kill the second tier of an organization’s leadership than the top tier.