Shallow Thoughts : : Jul

Akkana's Musings on Open Source Computing and Technology, Science, and Nature.

Sat, 31 Jul 2010

Bogus statistics on drug use among drivers

The "Roadshow" column in yesterday's Merc had some pretty ... odd ... statistics involving marijuana and driving.

It quotes "an NHTSA report" as saying:

contrary to popular belief, marijuana has been found to play a significant role in car accidents across the United States, with as much as 33 percent of drivers arrested at the scene of the accident being positive for marijuana and another 12 percent testing positive for marijuana and cocaine. Every year, 28 percent of drivers in the U.S. will attempt to drive within two hours after ingesting alcohol or illicit drugs. Marijuana is the drug used most often — 70 percent — by drivers who drove after drug use and is a major factor why crashes are the leading cause of death for American young people.

Whoa. Let's play that back again: 45 percent of all drivers arrested at accident scenes (33 plus another 12) test positive for marijuana? Nearly half?

Mr. Roadshow, you don't really believe that number, do you?

I didn't. So I did some searching, looking for the NTHSA source.

When I searched for large portions of the quoted phrase, I didn't find anything from the NHTSA. The Roadshow quote appears to come from an article on (I'm sure that's an unbiased source). Here's their MS Word file or Google's cached HTML version). The same article is also available as a PDF at and there are lots of other pages making reference to it.

The article cites "Brookoff, Cook & Mann, 1994; Sonderstrom, Dischinger, Kerns & Trillis, 1995." for the 33% number. There's no citation offered for the "28% will attempt to drive...". They credit "NHTSA, 2000" for "Marijuana is the drug used most often ... by drivers who drove after drug use", but that one's not important because it says nothing about prevalence in accidents, merely that it's used more often than other drugs (no surprise there).

The NHTSA weighs in

Googling on a more general set of terms, I found my way to a October 2000 NHTSA report, Field Test of On-Site Drug Detection Devices. It's a roundup of many different studies, with drug use numbers all over the map, though none larger than the 33% figure and certainly nothing near 45%. That 33% figure is near the bottom:

Brookoff et al. (1994) used on-site testing devices in a study that found a 58% prevalence rate for drugs in subjects arrested for reckless driving (who were not found to be impaired by alcohol). The Brookoff team found that 33% of their sample tested positive for marijuana, 13% for cocaine, or 12% for both. (Because of sampling flaws in the study, these drug test rates should not be interpreted as drug prevalence rates for reckless drivers.) Interestingly, the on-site device (Microline) used by Brookoff and his colleagues generated a significant false positive rate for marijuana when compared to GC/MS results.

The horse's mouth

So what about the original study? I wasn't able to find Dischinger, Kerns & Trillis, but here's Brookoff et al. at the New England Journal of Medicine: Testing Reckless Drivers for Cocaine and Marijuana (cookies required).

A couple of important notes on the study: the figures represent percentage of drivers arrested for "reckless driving that would constitute probable cause to suspect intoxication by drugs", who were not considered to be under the influence of alcohol, and who were suspected of being under the influence of marijuana or cocaine ("all patrol officers were told that they could summon [the testing van] if they stopped a person suspected of driving recklessly under the influence of cocaine or marijuana"). Morover, not all drivers consented to be tested, and the percentages are only for those who were tested.

Seems like a perfectly valid study, as far as it goes (though there's been some mild criticism of the test they used). It's mostly interesting as a study of how marijuana and cocaine use correlate with visible intoxication and sobriety test results. It's not a study of the prevalence of drugs on the road: the NHTSA report is right about that. The numbers it reports are useless in that context.

So the jump from that study to what and Roadshow implied -- that 45% of people involved in car accidents test positive for marijuana -- is quite a leap, and attributing that leap to the NHTSA seems especially odd since they explicitly say the study shouldn't be used for those purposes.

What really happened here?

So what happened here? Brookoff, Cook, Williams and Mann publish a study on behavior of reckless drivers under the influence of drugs.

NHTSA makes a brief and dismissive reference to it in a long survey paper.

Then writes an article that references the study but entirely misinterprets the numbers. This study gets picked up and referenced by other sites, out of context.

Then somehow the paragraph from shows up in Roadshow, attributed to the NHTSA. How did that happen?

If you look at the article, the paragraph cites Brookoff in its first sentence, then goes on to other unrelated claims, citing an NHTSA study at the end of the paragraph. I suppose it's possible (though hard to understand) that one could miss the first reference, and take the NHTSA reference at the end of the paragraph as the reference for the whole paragraph. That's the best guess I can come up with. Just another example of the game of telephone.

Nobody with any sense thinks it's a good idea to drive under the influence of marijuana or other intoxicants. But bogus statistics don't help make your point. They just cast doubt on everything else you say.

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[ 13:33 Jul 31, 2010    More headlines | permalink to this entry | comments ]

Thu, 29 Jul 2010

How to save on modeling fees

[Terrible's ad] At the Terrible's Sands Regency in Reno, Dave noticed this ad on the table in the room. "Wait -- isn't that the same guy, twice?"

Sure enough -- not just the same person, but the same photo, with different hair and neck pixeled in.

I guess Photoshop/GIMP artists are cheaper than photo models these days.

We spotted the same model in other ads around the hotel, sometimes masquerading as other races as well.

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[ 17:28 Jul 29, 2010    More gimp | permalink to this entry | comments ]

Wed, 28 Jul 2010

The Case of the Missing Gooseberry

Traveling always comes with risks. Aside from the risks you may encounter along the way, there are the worries of what you left behind. Will the house burn down? Will the mail pile up, signalling to thieves that the home is empty? Will the server stay up? On a more prosaic note ... Will the plants in the garden all die from lack of water?

Shortly before traveling to Oregon for OSCON, I acquired a cute little Cape Gooseberry seedling (courtesy of Mark Terranova at the south bay Geeknic). That's a new plant to me -- I'd never seen one before. But it was a cute little thing, and seemed to be flourishing. I had it in a pot on a little shelf where it would get morning sun but wouldn't get too hot in the afternoon, and was looking forward to planting it when it got big enough to withstand our marauding local seedling-loving snails.

[ Missing Cape Gooseberry ] To get it through my planned week-and-a-half absence, I had one of those glass watering bulbs they sell in drugstores. They're supposed to last several weeks, though they don't work that reliably in practice. Still, I saturated the soil with water the morning I left, then filled the bulb and crossed my fingers for no long heat waves.

I wasn't prepared for what I saw when I got back. Something had dug out my little gooseberry and taken it!

I still have no idea what got it. We certainly have some local squirrels who love to dig, and young squirrels (still learning their digging skills) love potted plants. But I wouldn't think a squirrel would have much use for a gooseberry seedling -- they just like the act of digging.

I wonder if cape gooseberry leaves are particularly tasty to rodents?

Ironically, the soil was still quite damp. The little plant probably would have made it through just fine.

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[ 14:17 Jul 28, 2010    More travel | permalink to this entry | comments ]

Wed, 21 Jul 2010

Writing scripts for your Canon camera with CHDK

On Linux Planet yesterday: an article on how to write scripts for chdk, the Canon Hack Development Kit -- Part 3 in my series on CHDK.

Time-Lapse Photography with your Inexpensive Canon Camera (CHDK p. 3)

I found that CHDK scripting wasn't quite as good as I'd hoped -- some of the functions, especially the aperture and shutter setting, were quite flaky on my A540 so it really didn't work to write a bracketing script. But it's fantastic for simple tasks like time-lapse photography, or taking a series of shots like the Grass Roots Mapping folk do.

If you're at OSCON and you like scripting and photos, check out my session on Thursday afternoon at 4:30: Writing GIMP Plug-ins and Scripts, in which I'll walk through several GIMP scripts in Python and Script-Fu and show some little-known tricks you can do with Python plug-ins.

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[ 10:31 Jul 21, 2010    More photo | permalink to this entry | comments ]

Wed, 14 Jul 2010

Hollow oranges

[hollow orange] Hollow oranges keep turning up on our lawn under the orange tree. Sometime we even find them still attached to the tree.

We're not sure what's eating them, but I have a theory.

A few weeks ago, I kept finding that as I walked across the backyard, something would fall out of one of the trees, either the orange tree or one of the guava trees. It was always barely viewed out of the corner of my eyes, but seemed about the size of a guava and fell and landed with about the same sound falling guavas make.

Only problem was: guava season is still three months away, and they haven't even started to grow on the tree yet.

I had speculations about what was going on, but I wasn't sure. Finally, a few days ago, I came out the office door and something fell out of the guava tree right in front of me.

It was guava sized, grey -- and furry, with a long naked tail. I got a good look at the mouse as it scooted across the grass to hide under the deck.

They're welcome to an orange now and then. We have lots of oranges. And they're polite about it -- they clean out one orange at a time rather than spoiling lots of them with small nibbles.

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[ 10:06 Jul 14, 2010    More nature | permalink to this entry | comments ]

Sat, 10 Jul 2010

Interactive arrow design in GIMP

How many times have you wanted an easy way of making arrows in GIMP?

I need arrows all the time, for screenshots and diagrams. And there really isn't any easy way to do that in GIMP. There's a script-fu for making arrows in the Plug-in registry, but it's fiddly and always takes quite a few iterations to get it right. More often, I use a collection of arrow brushes I downloaded from somewhere -- I can't remember exactly where I got my collection, but there are lots of options if you google gimp arrow brushes -- then use the free rotate tool to rotate the arrow in the right direction.

[GIMP Arrow Designer] The topic of arrows came up again on #gimp yesterday, and Alexia Death mentioned her script-fu in GIMP Fx Foundary that "abuses the selection" to make shapes, like stars and polygons. She suggested that it would be easy to make arrows the same way, using the current selection as a guide to where the arrow should go.

And that got me thinking about Joao Bueno's neat Python plug-in demo that watches the size of the selection and updates a dialog every time the selection changes. Why not write an interactive Python script that monitors the selection and lets you change the arrow by changing the size of the selection, while fine-tuning the shape and size of the arrowhead interactively via a dialog?

Of course I had to write it. And it works great! I wish I'd written this five years ago.

This will also make a great demo for my OSCON 2010 talk on Writing GIMP Scripts and Plug-ins, Thursday July 22. I wish I'd had it for Libre Graphics Meeting last month.

It's here: GIMP Arrow Designer.

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[ 11:25 Jul 10, 2010    More gimp | permalink to this entry | comments ]

Thu, 08 Jul 2010

Article: CHDK part 2

Part 2 of my series on hacking Canon point-and-shoot cameras with CHDK: Turn Your Compact Canon Camera Into a Super-Camera With CHDK, discusses some of CHDK's major features, like RAW image file support, "zebra mode" and on-screen histograms, and custom video modes (ever been annoyed that you can't zoom while shooting a video?)

Perhaps equally important, it discusses how to access these modes and CHDK's other special menus, how to load CHDK automatically whenever you power the camera on, and how to disable it temporarily.

Part 3, yet to come, will discuss how to write CHDK scripts.

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[ 17:27 Jul 08, 2010    More photo | permalink to this entry | comments ]

Wed, 07 Jul 2010

Huge brood of wild turkeys at Rancho San Antonio

[Wild turkey chicks scuffling] Late last week in the field next to the parking lots at Rancho San Antonio we had a chance to watch a wild turkey family foraging in the dry grass. Two adults and twenty chicks -- that's quite a brood!

Two of the chicks got into a scuffle and kept it up the whole time we watched them. The adults didn't seem interested, but some of the other chicks gathered round to see what was going on.

Photos: Wild turkeys.

Meanwhile, in other nature news, the hot weather has brought the odd unidentified chlorine smell back to the redwood forests. On the weekend, when we were having 90-degree days, the smell was very noticable around Purisima and El Corte de Madera, and on a few parts of Highway 9. Today, though the weather is cooler, the smell was everywhere on the Skyline trail at the top of Sanborn. Still no idea what's producing it.

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[ 20:23 Jul 07, 2010    More nature/birds | permalink to this entry | comments ]

Mon, 05 Jul 2010

Adventures with Virtual hosts and CGI on Apache 2.2

We had a server that was still running Debian Etch -- for which Debian just dropped support. We would have upgraded that machine to Lenny long ago except for one impediment: upgrading the live web server from apache 1 to apache 2.2.

Installing etch's apache 2.2.3 package and getting the website running under it was no problem. Debian has vastly improved their apache2 setup from years past -- for instance, installing PHP also enables it now, so you don't need to track down all the places it needs to be turned on.

But when we upgraded to Lenny and its apache 2.2.9, things broke. Getting it working again was tricky because most of the documentation is standard Apache documentation, not based on Debian's more complex setup. Here are the solutions we found.

Enabling virtual hosts

As soon as the new apache 2.2.9 was running, we lost all our websites, because the virtual hosts that had worked fine on Etch broke under Lenny's 2.2.9. Plus, every restart complained [warn] NameVirtualHost *:80 has no VirtualHosts.

All the web documentation said that we had to change the <VirtualHost *> lines to <VirtualHost *:80>. But that didn't help. Most documentation also said we would also need the line: NameVirtualHost *:80 Usually people seemed to find it worked best to put that in a newly created file called conf.d/virtualhosts. Our Lenny upgrade had already created that line and put it in ports.conf, but it didn't work either there or in conf.d/virtualhosts.

It turned out the key was to remove the NameVirtualHost *:80 line from ports.conf, and add it in sites-available/default. Removing it from ports was the important step: if it was in ports.conf at all, then it didn't matter if it was also in the default virtual host.

Enabling CGI scripts

Another problem to track down: CGI scripts had stopped working. I knew about Options +ExecCGI, but adding it wasn't helping. Turned out it also needed an AddHandler, which I don't remember having to add in recent versions on Ubuntu. I added this in the relevant virtual host file in sites-available:

  <Directory />
    AddHandler cgi-script .cgi
    Options ExecCGI

Enabling .htaccess

We have one enduring mystery: .htaccess files work without needing a line like AllowOverride FileInfo anywhere. I've needed to add that directive in Ubuntu-based apache2 installations, but Lenny seems to allow .htaccess without any override for it. I'm still not sure why it works. It's not supposed to. But hey, without a few mysteries, computers would be boring, right?

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[ 21:46 Jul 05, 2010    More tech/web | permalink to this entry | comments ]