|Cannabis doubles fatal crash risk?
||[03 Dec 2005|03:38am]
This is a good example of a bad study. Or at least, one that I don't
understand. "Cannabis doubles fatal crash risk" is the headline. The study says
The French National Institute for Transport and Safety Research found
evidence of cannabis use among 7% of drivers involved in fatal crashes.
Also, 2.9% tested positive for both cannabis and alcohol use. It is unclear
from the article whether that 2.9% is part of the 7% or in addition to it. A
doctor later in the article says "few" people tested positive for cannabis
How do they draw this conclusion without having testing results for drivers who
were not involved in fatal crashes?
Wait, they do claim that cannabis is found in 2.9% of all drivers. Where do
they get that from? To my knowledge, the test for cannabis is a little more
complicated than a roadside breathalizer, so I'm curious to find out where this
statistic comes from. It seems like they would only be able to collect samples
from people who already came into contact with law enforcement for some other
reason, in which case their results would not be very good for a "normal"