No, that recent marijuana and driving study didn't find that long-term users are worse drivers even when they haven't used recently.
Check out this @Forbes piece that quotes me abt what they did wrong (I will also start a thread): forbes.com/sites/janetwbu…
Check out this @Forbes piece that quotes me abt what they did wrong (I will also start a thread): forbes.com/sites/janetwbu…
@Forbes This was a tiny study - only 45 people with 16 in the control group and 28 in the MJ use group. They were pretty young and the controls were mostly women, MJ users were mostly men. Not well-matched. We always have to be careful of small studies due to generalizability.
@Forbes Also note- this was just a cross-sectional study of a moment in time. "Heavy use" was defined as saying they used over 1,500 times in their life, used 5/7 days in last week, tested positive for THC. However there was huge range of THC in urine: 480 ng/ml +/- 663 ng/ml (incs 0!!!)
@Forbes They did not drive real cars in the study- they used a simulator on a 19" screen. This must be a caveat when we make generalizations about real-time behavior in real vehicles.
@Forbes Cross-sectional comparisons between 2 groups are tricky because you have to control for confounding variables- other factors that could explain relationship between DV and IV. In this case, factors other than MJ use that could explain why performance differed.
@Forbes For instance, people who may become regular frequent MJ users may be different from non-users in ways that PRE-DATE their choice to use regularly. Maybe self-medicating things like pain, depression, anxiety, boredom, trauma, stress, impulsivity, etc.
None of these factors were accounted for in analysis except impulsivity. AND WHEN THEY DID, THE DIFFERENCES BETWEEN GROUP PERFORMANCE DISAPPEARED 
In my opinion, this already means I'm done with this study. It's too small at this point for me to want to go deeper in the analysis where they then compare 14 early-onset users and 14 late-onset users to 16 controls.
The reckless coverage of this study is alarming. It puts medical users, 'recreational' users (groups that overlap) at risk for discrimination. The slippery slope here is giving DMVs the idea that use history (even when NOT under the influence) is grounds to take away licenses.
We need more studies, longitudinal studies, better comparison groups, multiple instruments/measures for impairment and performance, etc.
