Later On

A blog written for those whose interests more or less match mine.

The Bathtub Fallacy and Risks of Terrorism

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Kenneth Anderson writes at Lawfare:

Bloomberg economics commentator Justin Fox is tired of being told that his chances of getting killed in a terrorist attack are (much) lower than his chances of slipping, falling, and dying in a bathtub. Implication being—suck it up, people, and quit being such irrational babies when it comes to assessing risks from terrorism.

Having also grown weary of hearing some version of this following terrorist attacks or government security responses, I was interested to find out why Fox (who’s a very smart guy) thinks such comparisons should be reckoned a bad form of argument.  Why does he think comparing fatal bathtub accidents and fatal terrorist incidents is fundamentally inapt, to the point of calling it “The Bathtub Fallacy”? (For those who don’t know his work, Justin Fox is a sophisticated business and financial journalist with a keen understanding of the literatures of statistics and risk assessment, and he’s also the author of the outstanding revisionist history of the “efficient market hypothesis,” The Myth of the Rational Market, 2009.)

What’s “The Bathtub Fallacy,” according to Fox? Following a terrorist incident or government counter-measure, he says (quoting a recent Financial Times (paywalled) column by its principal political columnist, Janan Ganesh), statistics are “dug out to show that fewer Westerners perish in terror attacks than in everyday mishaps. Slipping in the bath is a tragicomic favourite. We chuckle, share the data and wait for voters and politicians to see sense.” To this Fox adds:

Sure enough, a couple of days later [after Ganesh’s column], there was Nicholas Kristof in the New York Times, making Ganesh’s point for him: “The bottom line is that most years in the U.S., ladders kill far more Americans than Muslim terrorists do. Same with bathtubs. Ditto for stairs. And lightning.” Now, I love statistics. I cite them and sort them and chart them all the time. I even wrote a whole column last month about various causes of untimely death in the U.S. But I agree with Ganesh that comparing annual deaths due to bathtubs and terrorism is a mistake.

The urtext of ordinary accident/terrorism comparisons might be the 2009 book by political scientist John Mueller, Overblown: How Politicians and the Terrorism Industry Inflate National Security Threats, and Why We Believe Them.  (Note: Mueller has been an occasional Lawfare contributor, along with his co-author Mark Stewart—quite graciously, given the distance between his views and what I’d describe as the mean of Lawfare posts on these topics.)  Overblown was widely noticed and debated when it appeared in 2009 at the beginning of the first Obama term, and it has remained a book popular among strands of the American left and libertarian right seeking debunking arguments by which to critique the post-9/11 national security apparatus.

Over time versions of the “bathtub” argument have become a bit of a go-to-meme among some journalists and public policy pundits.  It pops up with clock-work regularity each time there’s a terrorist attack, whether in the U.S., Europe, or elsewhere.  But what’s wrong with it?  Maybe it’s correct and useful and not a “fallacy” at all; after all, John Mueller is also a smart guy and he doesn’t think it’s bad reasoning.

This Readings post focuses on the Fox column, however, and the column gives three reasons why Fox thinks the comparison with bathtub slip-and-falls is mistaken and why terrorism is different (it will surprise no one that I broadly agree with them).  The three reasons:

First … terrorism is designed to, you know, sow terror. As Ganesh writes, most people can “intuit the difference between domestic misfortune and political violence. The latter is an assault on the system: the rules and institutions that distinguish society from the state of nature. Bathroom deaths could multiply by 50 without a threat to civil order. The incidence of terror could not.”

Second is that ladders, stairs and bathtubs are undeniably useful. Terrorists, not so much ….

Finally, comparing the incidence of terrorism with that of common accidents is an incompetent and irresponsible use of statistics. Household accidents are lots and lots of small, unrelated events. As a result, while individual accidents can’t be predicted, the overall risk is easy to quantify and is pretty stable from year to year.

Note that each of these reasons aims to show that the risks of the bathtub are different from those of terrorism solely on the basis of the real-world consequences of these events—real-world harms—and not as a matter of each category’s “intrinsic” morality (as many would frame the difference).  There might also be (and for many, most, perhaps nearly all of us, there is) an “intrinsic” moral difference between these two, but Fox’s three reasons broadly fit within “consequentialist” rather than “deontological” ethics. They are situated within the standard utilitarian framework of economists—the standard public policy framework that seeks to identify, and to the extent possible quantify, real-world harms which, whatever else one might want to say about a category such as terrorism, serve to establish a common denominator for policy upon which even those with differing moral views can agree.

Hence, when Ganesh differentiates between mere “misfortune” and “political violence,” he does not argue that political violence is different (for purposes of comparing risks) because of its wickedness as such—that is, because of its intrinsic morality. What matters for comparative policy purposes are the harms terrorism brings about (including the knock-on and remote ones it threatens to bring about). There are fundamental differences between ordinary accidents and terrorism—apart from any judgments of their comparative morality.

Taken together, Fox’s three reasons constitute a quite sweeping indictment of The Bathtub Fallacy; together they also encompass, in a few short sentences, a wide range of ethical and social claims. (I will say more in a follow-up post about the first reason—the threat to institutions that undergird a society’s common social life.)  Fox’s column goes on, however, to focus on the third reason—what he regards as the bad use of statistics in making these comparisons in the first place:

Terrorism is different. There are small incidents, but there are also huge ones in which hundreds or thousands of people die. It’s a fat-tailed distribution, in which outliers are really important. It also isn’t stable: Five or 10 or even 50 years of data isn’t necessarily enough to allow one to predict with confidence what’s going to happen next year. It’s a little like housing prices—the fact that they hadn’t declined on the national level for more than 50 years before 2006 didn’t mean they couldn’t decline. Meanwhile, the widespread belief that they wouldn’t decline made the housing collapse more likely and more costly.

The conclusion that terrorism is different relies importantly on Fox’s characterization as a “fat-tailed distribution” of risks.  Fox cites Nassim Nicholas Taleb’s (of Black Swan fame) extensive writing on this, but then moves on to an interview Fox conducted with Carnegie Mellon University professor Baruch Fischhoff in researching this column.  Who’s Baruch Fischhoff, you ask? Well, among (many) other things, Fischhoff is a “past president of the Society for Risk Analysis, past member of multiple national and international commissions on the risks of terrorism and other bad stuff, and author of lots of books with ‘risk’ in the title.”  Also, Fox adds, he was Daniel Kahneman’s former research assistant at the Hebrew University of Jerusalem in the early 1970s, and thus someone “present at the creation of the school of psychological research that has shown how bad we humans can be at processing probabilities.”

“People who just look at the average are doing the analysis wrong,” Fischhoff tells Fox.  Fischhoff does not think, either, that “it’s irrational to fear terrorism more than falling in the bathtub.” Why? It’s different in terms “of the uncertainty and the shape of the distribution, how well we understand it and the possibility of these large-scale events.”  Moreover, Fischhoff adds, in another deceptively simple observation, that “people tolerate risks where they see a benefit.”

While that last point might appear to be a mere truism, it sheds light on how risk analysis fits into cost-benefit analysis.  In public policy analysis, at least, risk analysis is relevant because it tells us not just about determinate costs and benefits, but about . . .

Continue reading.

Written by LeisureGuy

14 April 2017 at 1:16 pm

Posted in Science, Terrorism

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