The WSJ today, in the form of the always excellent Carl Bialik, digs a little deeper on the ongoing contretemps between Mothers Against Drunk Driving and the Century Council, which revolves around the issue of whether drunk-driving enforcement should center on the most intoxicated drivers (who, the Council argues, do most of the damage), or widen the net to include impaired drivers on various levels (who, as MADD argues, still do plenty of damage). Underlying the dispute is the fact that, after significant drops in alcohol-related fatalities in the U.S., the number has been steady for the last few years. Also worth considering is that, as the piece notes, “researchers estimate that there is just one drunken-driving arrest for every 80 to 300 trips taken by drunken drivers.”

A few interesting tidbits:

Paul Zador, a statistician at the research company Westat, has compared the blood-alcohol levels of drivers killed in crashes with levels of drivers stopped for random roadside testing during peak drunken-driving hours. That helped him estimate how likely it is that an extra drink will prove fatal. Compared with sober drivers, drivers at 0.15 or higher were about 400 times more likely to die in a crash. Drivers with levels between 0.10 and 0.14 were 50 times more likely than sober drivers to die in a crash.

But as Bialik notes,

These troubling rates, cited by the Century Council in its campaign against hard-core drunken drivers, might overstate the role of alcohol in killing heavy drinkers. As Dr. Zador notes, the same personality traits that lead to driving while highly intoxicated are probably tied to other risky behavior behind the wheel. These drivers are likely dangerous even before they have had their first sip.

And lastly:

In a 2002 study co-authored by Susan Baker, a professor at Johns Hopkins University’s Bloomberg School of Health, researchers drew upon an intriguing data source: interviews with surviving family members of 818 victims of fatal crashes.

The next of kin painted a frightening portrait of those dead drivers with a BAC of 0.15 or higher: 55% were described as drinking and driving at least once a month. But those whose blood-alcohol level was between 0.10 and 0.14 — and thus mostly wouldn’t have qualified as hard-core — weren’t much safer: 35% drove drunk at least monthly. “We shouldn’t simply be focusing on ‘hard-core’ drivers,” Prof. Baker says.

As an aside, there is something interesting, and of course disturbing, in the regularity of impaired-driving fatalities, particularly given all the random variables — who decides to drink and drive, how much, how many other people are on the road at that time, who gets caught and who doesn’t, what roads they travel on, etc. I thought of a passage from Leonard Mlodinow’s book The Drunkard’s Walk, an absolutely essential tome for the statistics-impaired such as myself, talking about aggregate versus individual behavior. “We associate randomness with disorder,” he writes. “Yet although the lives of 200 million drivers vary unforeseably, in the aggregate their behavior could hardly have proved more orderly.” He quotes Kant: “Each, according to his own inclination, follows his own purpose, often in opposition to others; yet each individual and people, as if following some guiding thread, go toward a natural but to each of them unknown goal; all work toward furthering it, even if they would set little store by it if they did know it.”

(thanks Jack)

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