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Based only on the abstract (the text is behind a paywall), it appears the first paper only discusses "the drivers' risk of being killed in a fatal crash", and not overall crash incidents, which is the point of your first sentence.

In addition, the abstract's conclusion starts "Although overall, drugs contribute to crash risk regardless of the presence of alcohol, such a contribution is much lower than that by alcohol." (Emphasis mine.) This seems to contradict your statement that there is not an increased risk with marijuana use. (The NYT article seems to confuse the two when it talks about "risk of a fatal accident" in one paragraph then "risk of a crash" in the second.)

Instead, I think the paper you want, which is a bit older (from 2012) but not behind a firewall, is http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3276316/ . It says:

> Experimental studies have shown modest functional impairment, but debate exists over how well these experimental studies translate into real-life driving situations (41). Epidemiologic studies, however, have shown contradictory results (39, 42, 43). ... it is unclear whether marijuana plays a significant role in crash causation.

The paper itself is a meta-analysis. They write:

> Results of this meta-analysis indicate that marijuana use by drivers is associated with a significantly increased risk of crash involvement. Specifically, drivers who test positive for marijuana or self-report using marijuana are more than twice as likely as other drivers to be involved in motor vehicle crashes.

It then very emphatically points out that this conclusion is not strong enough for public policy decisions, and that there are many possible confounding factors.

This conclusion is also mentioned in the NYT link you posted: "Still, it is clear that marijuana use causes deficits that affect driving ability, Dr. Huestis said. She noted that several researchers, working independently of one another, have come up with the same estimate: a twofold increase in the risk of an accident if there is any measurable amount of THC in the bloodstream."

Thus, I think it's enough to suggest that your first line is likely incorrect.




I took the NYT quote from Eduardo Romano to mean that after controlling for some of those confounding factors, there was no evidence of increased risk. I posted the NYT article because the abstract didn't mention much about marijuana specifically.

Specifically, drivers who test positive for marijuana or self-report using marijuana are more than twice as likely as other drivers to be involved in motor vehicle crashes.

Without having read the study, do you know if this statistic controls for age or anything else? If so, I stand corrected.

Thanks for your polite tone, it's not every day I get called a "fucking moron" before 7 a.m. :)


Like I said, I think the NYT quote confuses two points - no evidence for increased driver fatalities; and evidence for increased number of accidents. While I can understand how you made the inference you did, as I pointed out, elsewhere in the same NYT article points out that the accident rate is 2x that of other drivers, so there is an internal inconsistency. The simplest correction which makes it match external evidence is assume that the Romano quote omitted the "fatal" accidents context.

The study I linked to says: The data were stratified and analyzed according to study design, type of drug assessment, study time period, study location, or age of the study subjects. A more than 2-fold increased crash risk associated with marijuana use was found in each of the subsets of studies

Table 2 shows the age breakdown as "<25" and "all ages." See http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3276316/table/tb... .




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