From this working paper by the Center for Strategic and International Studies:

The US must plan its Homeland defense policies and programs for a future in which there is no way to predict the weapon that will be used or the method chosen to deliver a weapon which can range from a small suicide attack by an American citizen to the covert delivery of a nuclear weapon by a foreign state. There is no reason the US should assume that some convenient Gaussian curve or standard deviation will make small or medium level attacks a higher priority over time than more lethal forms.

Any structured intellectual approach to describing this situation -- and planning for it -- is so uncertain that a valid structure can only be developed as an exercise in complexity or "chaos" theory.

I, however, would like you to think about the biological threat in more mundane terms. I am going to suggest that you think about biological warfare in terms of a TV show called "Buffy the Vampire Slayer," that you think about the world of biological weapons in terms of the "Buffy Paradigm," and that you think about many of the problems in the proposed solutions as part of the "Buffy Syndrome."

Finally! All those hours of research are beginning to pay off!