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Considered harmful considered harmful

“In a roadside study, one in three reckless drivers who were tested for drugs tested positive for marijuana. It’s more harmful than we all thought.”

Gnrgh! Meaningless! How many other drivers tested positive for marijuana? Was the ratio of reckless to non-reckless drivers different for those testing positive than those testing negative? Were all the reckless drivers stopped tested? The language quoted implies that they weren’t, so what factors determine who were tested and who weren’t?

You know what’s harmful? Public awareness campaigns that encourage people to think sloppily about statistics, that’s what. These are the basic tools we need in order to make sense of the flood of information all around us, and ads like this rely on our failure to understand elementary statistics and survey methods. Pisses me off, if that wasn’t obvious.

3 Comments

  1. Incidentally, here‘s the abstract for that study. To answer the questions in order: No other drivers were tested. No data. Unclear from the abstract – “A total of 175 subjects were stopped for reckless driving, and 150 (86 percent) submitted urine samples for drug testing at the scene of arrest”; this article (which raises other serious questions about the methodology of this study) implies that the 5 who were not tested did not consent.

    Without paying the $10 to see the full text of the study, I’ve got to say I have no confidence in any of the results. As for the interpretation of the results, the other article puts it pretty well: “This study falls prey to the fallacy that correlation equals causation. Not knowing the total number stopped for reckless driving makes it impossible to support the authors’ conclusion that the use of marijuana and cocaine is a major cause of reckless driving.”

  2. Hey, nice digging. Thank you.

  3. Michael Harshberger Michael Harshberger

    I agree…this commercial was bullshit. I can’t possibly convey how upset this made me! I mean, come on, really…it’s as if our country’s infamous “war on drugs” doesn’t waste enough of our valuable resources. If we’re going to invest in a lost cause, we should at least provide the public with intelligible statistics. A large number of people testing positive for a substance (i.e. marijuana) doesn’t mean that it’s harmful; it simply means that it’s popular. So tell us something we don’t know. Besides, how can one conclude that a driver who tests positive for marijuana was high at the time he/she was driving? Even an uneducated American probably knows that marijuana lingers in urine for a average of 30 days; just because I got pulled over and tested positive for pot doesn’t mean I was ‘smoking and driving.’ With all the money that we allocate to the NIDA, I would think they would find someone with a brain to edit their announcements…

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