[tacticalogic]

"the prevalence of nonalcohol drugs reported in this study should be interpreted as an indicator of drug use, not necessarily a measurement of drug impairment."

So basically it shows that they detected more people who've smoked pot. Did the people change, or did the testing change (or maybe both)?

[petitfour]

Or it shows pot smokers are just really bad drivers and/or have little concern for themselves or others.