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Cooperation and the common enemy effect


  • K.J.M. De Jaegher
  • B. Hoyer


This paper presents a game-theoretic rationale for the beneficial effect of a common enemy on cooperation. In a defence game against a common natural threat, the value of the public good of defence is equal to the sum of the players’ defensive efforts. The game therefore takes the form of a prisoner’s dilemma, leading to free-riding. When the same defence game is played against a common enemy, the value of the public good of defence is equal to the smallest defensive effort. The game now takes the form of a stag hunt, so that a cooperative equilibrium becomes possible. For this reason, an informed and benevolent government may not want to inform the public that it is facing a common natural threat rather than a common enemy. At the same time, the common enemy has an incentive to mimic nature, and perform only random rather than targeted attacks.

Suggested Citation

  • K.J.M. De Jaegher & B. Hoyer, 2012. "Cooperation and the common enemy effect," Working Papers 12-24, Utrecht School of Economics.
  • Handle: RePEc:use:tkiwps:1224

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    References listed on IDEAS

    1. B. Hoyer, 2012. "Network Disruption and the Common Enemy Effect," Working Papers 12-06, Utrecht School of Economics.
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    Common Enemy Effect; Defence Games; Prisoner’s Dilemma; Stag Hunt;

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