February 10, 2015

Pot less dangerous than alcohol in driving

Hit & Run - Although laboratory testing indicates that marijuana impairs driving ability, the effects are not nearly as dramatic as those seen with alcohol, and measuring the real-world consequences has proven devilishly difficult, as demonstrated by a landmark study that NHTSA released . In "the first large-scale [crash risk] study in the United States to include drugs other than alcohol," NHTSA found that, once the data were adjusted for confounding variables, cannabis consumption was not associated with an increased probability of getting into an accident.

The study included more than 3,000 drivers who were involved in crashes during a 20-month period in Virginia Beach, Virginia, plus 6,000 controls who drove in the same area during the same period but did not get into accidents. As usual, the study found that alcohol use was strongly correlated with crash risk. After adjustment for confounding, the crash risk for drivers with a blood-alcohol content of 0.08 percent was twice the crash risk for sober drivers; it was six times as high for drivers with a BAC of 0.10 percent and 12 times as high at a BAC of 0.15 percent. But the picture for marijuana was quite different.

Over all, drivers who tested positive for active THC were 25 percent more likely to be involved in crashes. But once the researchers took sex, age, and race/ethnicity into account, the risk ratio shrank from 1.25 to 1.05 and was no longer statistically significant:

This analysis shows that the significant increased risk of crash involvement associated with THC and illegal drugs...is not found after adjusting for these demographic variables. Further adjusting for alcohol consumption made the crash risk of cannabis consumers equal to that of drivers who tested negative for alcohol and all other drugs. In other words, the study provides no evidence that marijuana use increases crash risk. Furthermore, the authors note, that result is similar to what the best-designed previous studies have found: a small or nonexistent increase in crash risk.

3 comments:

Anonymous said...

"Say you get in a car accident, and you've been smoking pot. You're only going four miles an hour." - Bill Hicks
https://www.youtube.com/watch?v=t9R2vObtYVI

Anonymous said...

Which only proves the old adage that there are lies, damned lies, and statistics.
If the pot is any good, you get fucked up, and when you're fucked up you shouldn't be driving.
Just what is exactly meant by 'adjustment for confounding' anyway?
Estimating spurious relationships between variables is a great manipulative device for generating bull shit.

Anonymous said...

I haven't smoked any pot in about 30 years but I can recall that adding alcohol to a pot high had a MAGNIFYING effect. My biggest concern is that drivers will overdue BOTH TOGETHER.