Is it worth more to save a person from a terrorist's bomb than, say, a car crash? John Mueller and Mark Stewart grapple with the spending choices we make in their new book about homeland security. The trouble, of course, is that much of what matters to us is unmeasurable. In the United States, we lose some 34,000 people a year in highway accidents. If we lost even a thousand a year--twenty per week--in terrorist attacts, the country would be likely be paralyzed by fear (and I can only imagine where that would take our politics.)

Yet somehow we're able to pack the minivan, load the kids, jack up the radio, and head out onto deadly highways. Driving is a risk we're willing to accept. We feel safe even when we're not. And feeling safe, it can be argued, matters more within a society than numbers. Even if researchers made a convincing case that we could reduce deaths by 10,000 or 15,000 a year, I bet most people wouldn't support increased spending for it. That's because they (we) don't feel threatened--even if we should.

Still, we spend lavishly on counterterrorism. And in the post 9/11 fervor, which was revisited on its 10th anniversary, much of the spending has gone unquestioned. That's going to change. I don't think we'll ever look at the numbers as coldly as Mueller and Stewart, who use the logic of a triage ward. I'm not convinced that we should. But their analysis provides a good starting point.