Fishy Science

Posted on December 2, 2005 by Pete Guither

Thanks to scottp, comes this breaking news from New Scientist: Cannabis doubles the risk of fatal crashes.
Now since all the reliable data I’ve found indicates that, while smoking pot while driving is a bad idea, it actually causes drivers to be cautious and is actually safer than driving while fatigued, or any of a host of other distractions. So the alarmist nature of this article aroused my curiosity, especially these statements:

“These shocking results prove beyond doubt the dangers of drug-driving, and of mixing drink and drugs before getting behind the wheel,” says Mary Williams, chief executive of Brake, the UK’s national road safety charity. [read MADD]

“We need to see the government doing targeted, prime-time TV advertising on the issue of drug-driving, and we … need to see a national roll out of roadside drugs-testing by the police to catch drug-drivers before they kill or injure innocent road users.”

Whoa. Just what did this study discover?
Let’s look. I’m quoting extensively so you can get a real feel for the extent of this ‘scientific reporting.’

Cannabis almost doubles the risk of fatal car crashes, according to a new study, though smoking the drug is still far less risky than drink-driving, the researchers say.

Stoned drivers were almost twice as likely to be involved in a fatal car crashes than abstemious drivers, according to a study of 10,748 fatal car crashes in France between 2001 and 2003. More than half of the drivers in the study themselves died as a result of their accidents and all the subjects were tested for drug and alcohol use after crashing.

Even after accounting for factors such as the age of the drivers and the condition of the vehicle, the researchers conclude that cannabis caused a significant number of the fatalities, with 2.5% of the crashes directly attributed to cannabis use. Alcohol was the direct cause of about 29%.

Using cannabis and alcohol together was 16 times more risky than driving with neither drug in their body.

“You are more likely to be involved in a crash, probably because of the drug‰s effect on your reaction times and concentration,” says Jean-Louis Martin who carried out the research at the UniveristÚ Claude Bernard in Lyon, France. “But the drug also makes you more vulnerable to the effects of the crash, so you are more likely to die.” The study did not explore why cannabis smokers fair less well in a crash.

There are so many questionable assumptions in this piece that I have absolutely no idea whether there is a lick of real science involved. I do see that cannabis is somehow “responsible” for 2.5% versus 29.0% for alcohol, which certainly doesn’t make cannabis look very bad. And the “more vulnerable to the effects of the crash” stuff? — WTF??
If anybody can track down an English version of the actual research or an abstract from it, please let me know. I have a feeling that we’ll be seeing this quoted by prohibitionists without them having a clue to the actual methodology, and I want to be prepared.
Update: Thanks to everyone who tracked down information. I’ve spent some time reading the study, and I lack the skills to completely parse everything in it.
There were, however, a couple of questionable assumptions used. For example, the study assumes that the prevalence of cannabis use within the overall driving population could be accurately represented by analyzing those drivers involved in minor injury crashes (and this is critical to forming an odds analysis of responsibility). I’m not so sure that it’s a reasonable assumption. Additionally, I question some of the decisions used in determining responsibility for fatal crashes, and groups excluded.

This entry was posted in Uncategorized. Bookmark the permalink.