yet another idea of mine gets published before I write it

Actually, I generally view that sort thing as meaning I tend to have good ideas at least. Anyway, I won't lose sleep over this one, since it isn't in my discipline at all, but a new study proposes that the best defense against terrorism is, essentially, no defense at all:

The premises:

1. The number of potential terrorist targets is essentially infinite.

2. The probability that any individual target will be attacked is essentially zero.

3. If one potential target happens to enjoy a degree of protection, the agile terrorist usually can readily move on to another one.

4. Most targets are "vulnerable" in that it is not very difficult to damage them, but invulnerable in that they can be rebuilt in fairly short order and at tolerable expense.

5. It is essentially impossible to make a very wide variety of potential terrorist targets invulnerable except by completely closing them down.

The policy implications:

1. Any protective policy should be compared to a "null case": do nothing, and use the money saved to rebuild and to compensate any victims. [emphasis added]

2. Abandon any effort to imagine a terrorist target list.

3. Consider negative effects of protection measures: not only direct cost, but inconvenience, enhancement of fear, negative economic impacts, reduction of liberties.

4. Consider the opportunity costs, the tradeoffs, of protection measures.

Absurdly attentive readers will remember that I was all over this idea ages ago.

(via Megan McArdle)