Comments on: Friends Don’t Let Friends Walk Drunk

By: Bob

Bob — Mon, 07 Dec 2009 21:55:15 +0000

All of these posts arguing that per-mile data is invalid. While there are many problems with the statistics here, one has to examine the original reason for posing the question in the book, which is: If you live one mile from the party you get drunk at, is it safer to walk or drive home? In such a scenario, an analysis PER MILE is indeed the most valid statistic for comparison. Such an analysis is probably most relevant to city-dwellers, where a reasonable walking distance between bar/club/party/etc. and home is more likely.

Of course, the real statistical problems come in then if city-dwellers are indeed more likely to have such a choice. How does that affect the statistics comparing drunken deaths by walking/driving in urban versus rural areas? Certainly the chances of getting killed walking home drunk in a rural area are different from an urban area, and certainly the percentage of people who do walk home drunk in a rural area is different from that in an urban area. And that’s just the start of the difficulty, since city-dwellers would probably take a cab or public transport part of the way rather than walking all the way home, making the stated scenario in the book seem rather unlikely.

However, despite all of these problems, the per mile basis of analysis is NOT fundamentally flawed, as so many posts are claiming. It’s just only applicable to a certain situation as defined in the scenario of the book… the many problems come in evaluating the validity of that scenario and collating the correct statistics. But to answer that particular scenario, the per-mile analysis is the correct one.

By: Kapil

Kapil — Sat, 21 Nov 2009 08:41:41 +0000

Like they normalized per mile, shoudn’t they futher normalize drunk driving and drunk walking death by the average rates of deaths by traffic during walking or driving?

By: mikey2gorgeous

mikey2gorgeous — Mon, 12 Oct 2009 12:53:42 +0000

The per mile data is not completely invalid. The per hour rate doesnt take into account that a 3 mile journey will take a pedestrian an hour compared to a few minutes in a car. Neither measure is an absolute figure - they must BOTH be taken into account and this is not easy data to do that with.

In the UK per hour walking is safer than cycling. Per mile cycling is safer.

I would be tempted to read the book before commenting, these guys are pretty good a stats!

By: gpsman

gpsman — Sat, 10 Oct 2009 03:09:33 +0000

” one could be standing on a street corner after having had a few drinks, and be killed by an out-of-control taxi (or a hit-and-run driver), and this would be coded as a pedestrian alcohol-impaired crash”

I didn’t know there was any such code… but I didn’t know pedestrians could crash.

Perusing MMUCC (Model Minimum Uniform Crash Criteria, 3rd Ed., 2008, DOT HS 810 957) I see no such reference.

AFAIK, in the US, a guy could have a half a beer and be hit in a crosswalk by a stone sober driver and, if that half beer is mentioned to the investigating officer, we have an “alcohol related incident”.

By: Tom Vanderbilt

Tom Vanderbilt — Fri, 09 Oct 2009 21:02:01 +0000

I’m glad you’ve all chimed in the “per hour” note; as I mentioned in the original post, one of the main problems is exposure data — and one problem with that is just how to measure it (not to mention all the other issues, like individual risk versus aggregate risk). And yes, you might drive five miles but not walk five miles, but you also wouldn’t walk at 55 mph — so it’s not inconceivable to think the rates would actually sync up in some cases. In any case, the science and data on “per hour” crash rates is hardly conclusive and needs much further examination; as a paper by Sonkin and Edwards, et al, in the Journal of the Royal Society of Medicine notes, “in other studies, comparisons of fatalities per hour and for distance suggest that walking and cycling still have higher risks than car transport, but that the differential is not so great.” But the differential exists.

By: Fred Freedom

Fred Freedom — Fri, 09 Oct 2009 19:37:22 +0000

What the others said: a “per mile” comparison for walking/biking/driving is completely invalid, as not too many people walk 10, or 20 or 60 miles a a day. Slightly shocking that this blog would not make this clear. A per-hour comparison would make sense… but would not make cars seem safer and walking seem dangerous, which seems to be the point of the mis-interpretation.

By: Jon Swerens

Jon Swerens — Thu, 08 Oct 2009 16:49:40 +0000

You mention “more than 1,00 drunk pedestrians.” Did you mean “100″ or “1,000″?

By: DE

DE — Wed, 07 Oct 2009 23:50:06 +0000

Tom,

I am disappointed in this blog for the first time. SteveL appears to have beaten me to this, but you have fallen for the classic Randal O’Toole “per mile comparison” fallacy. The simple fact that walkers are more likely to start a short 1-3 mile trip than a 15-20 mile trip means that every time a drunk driver completes a long trip, he skews the deaths/mile statistic wildly in favor of car drivers. We can argue with little doubt that most drunk trips on foot are college students and urbanites walking very small distances. They probably complete many trips safely that would hardly register in a miles to miles comparison. Since many would object to a trip vs. trip comparison that would bias in favor of urban trips, I suppose an hour to hour comparison would be the best method.

By: SteveL

SteveL — Wed, 07 Oct 2009 21:05:04 +0000

* the fact that drunk people are staggering home at the same time as drunk drivers may be a factor -especially at night. You’d need to compare danger to sober pedestrians journeying in the same areas at the same times.

* Per mile is a bogus measure, as it baises towards long-distance car/train journeys; per hour measures your risk per hour of use of a transport.

* here in the UK we have less of a drunk driving problem on account of having lots of pubs in walking distance in our cities. I have two establishments reachable without crossing any roads at all, for which I am very grateful

By: Charles

Charles — Wed, 07 Oct 2009 20:16:25 +0000

Are deaths miles traveled a good comparison?

I would drive 5 miles but I wouldn’t walk 5 miles.

Maybe deaths per time spent traveling is a better comparison?