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Studies linking marijuana and traffic accidents show contradictory findings 

click to enlarge Impaired driving is worthy of inquiry. - LANAELCOVA / SHUTTERSTOCK.COM
  • LanaElcova / Shutterstock.com
  • Impaired driving is worthy of inquiry.

Everyone wants to know how legalization is going in Colorado.

Both inside and outside the state, people are fixated on gleaning what they can from the first few years of retail marijuana sales. And while many will always insist the sky has fallen (pretty sure it hasn't) and others will only see a 420 paradise (also not seeing it), there's still a wide swath of reasonable types in the middle who nonetheless form conclusions first and find supporting evidence second.

Problem is, there's sometimes evidence out there to support different conclusions. Take the question: Has marijuana use among youth gone up or down in the legal era? There are commonly cited studies that "prove" both answers. People pull them out to justify whatever point they're trying to make.

Now we have another case of conflicting data on our hands, this time in regard to another public safety question: Has marijuana legalization caused more impaired-driving incidents? A new report on the matter from the Highway Loss Data Institute (HLDI), funded by insurance companies and associations, analyzed collision claims which those involved in a car crash submit to their auto insurer. Report authors used data from January 2012 through October 2016 to analyze collision claim rates in Colorado, Washington and Oregon (where recreational marijuana is legal) compared with control states chosen for geographic proximity — Idaho, Montana, Nevada, Utah and Wyoming. (Note that Nevada and Montana allow medical marijuana and Wyoming and Utah allow a more limited use of medical marijuana.) Controlling for "differences in the rated driver population, insured vehicle fleet, the mix of urban versus rural exposure, unemployment, weather and seasonality" in unspecified ways, they found that "the legalization of retail sales was associated with a 2.7 percent increase in collision claim frequencies."

We at CannaBiz are not scientists, but we're pretty sure we heard somewhere that correlation doesn't equal causation. Are we high or is there no data or information linking collision claims with marijuana use in this study?

No matter, the study was trotted out in local, state and national media, where journalists slapped on catchy headlines to let people know they're right to be scared of marijuana. Sigh.

This new study doesn't align well with research showing medical marijuana laws are associated with a decrease in car-related fatalities. Take the 2012 study, "Medical Marijuana Laws, Traffic Fatalities, and Alcohol Consumption" by economics professors from Montana State University, University of Oregon and University of Colorado-Denver (and funded by those institutions) as an example. They pulled data from the Fatality Analysis Reporting System (FARS) between 1990 and 2010 for the 14 states (and the District of Columbia) that had medical marijuana laws on the books at the time. From that sample, researchers found that "The first full year after coming into effect, the legalization of medical marijuana is associated with an 8 to 11 percent decrease in traffic fatalities," but that the most significant effect was among fatalities linked to alcohol use. Their theory for that? With legal access to marijuana, people choose pot over alcohol and fewer accidents result. But, complicating matters even further, alcohol sales are up in Colorado since legalization.

So, in a post-fact world, the takeaway here is not "just choose your study and keep believing whatever you want to believe." You have the power to check sources, research funders and analyze methodology. So before latching onto every "studies show" line that agrees with your views, use that brain of yours to do your due diligence.

Or, just keep reading CannaBiz and we'll do it for you.

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