No study needed. Stoned Drivers Pose Deadly Threat

An editorial in the Boston Herald proclaimed “No study needed: Stoned drivers pose deadly threat.”

The Associated Press recently disclosed the results of two new studies attempting to determine the impact on traffic deaths in states that have legalized recreational marijuana. Both suggested that laws legalizing recreational marijuana may lead to more traffic fatalities.

We wouldn’t think a comprehensive study would be required to reach that conclusion…

We don’t need high-brow medical research to realize that in Massachusetts and other recreational-pot states, your chances of running into a substance-impaired motorist can only increase.

And that collision could cause serious injury or death.

I was the lead author of one of the papers they referenced. We found a 20% increase in number of traffic fatalities in the first 4 states to legalize recreational marijuana. We calculated that if every state legalized marijuana, there would be 6800 excess deaths each year. Yet, I agree with the Boston Herald. It shouldn’t require linear regression difference-in-difference analysis of panel data to prove the obvious. If more people use an intoxicant, there will be more impaired drivers which will lead to more roadway fatalities. The only surprise was the magnitude of the number of deaths. 

It only took a quick look at the US DOT traffic fatality database to see that fatalities increased in states after they allowed commercial sales of recreational marijuana. But, I had to enlist the help of a Harvard math student to put the information in a way that would satisfy a scientific journal, replete with regression coefficients, confidence intervals and p values. 

Even then, the first peer reviewer complained that our results were “simply not plausible.” Well, our study is not only plausible, it is accurate. The majority of laypeople, like the Boston Herald editorial staff, don’t even think our findings were newsworthy because they were expected. My brother falls into that category. I was so proud of getting my paper published in a top journal, I called my brother the lawyer. Bursting my bubble, my older brother told me without hesitation, “Big deal. Of course fatalities go up.” 

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