We conduct experiments to test the collective action dilemmas associated with defensive and proactive counterterror strategies. Defensive policies are associated with creating public 'bads' (e. g., a commons) whereas proactive policies are akin to the voluntary provision of public goods. When combined, the inefficiency of collective action is exacerbated, resulting in a situation known as a Prisoner's Dilemma squared (PD2). Deterministic versus probabilistic equivalent versions of the associated externalities are compared within a laboratory setting. Experimental results reveal that the collective action problem associated with counterterror strategies is deepened in uncertain environments, and is indeed a robust regularity that is not easily overcome; as individuals gain more experience, they become even more self-interested. 2011 Springer Science+Business Media, LLC.
