That's just fine, I agree with that study. Doesn't prove that smokers are idiots however.
Furthermore I'll step up and be the 'stoner' that clears up the charges thing for you.
It varies by state, those that have decriminalized marijuana for medicinal uses have also a higher ammount to warrant jail time, for example North Carolina is 42.5 grams (ounce and a half) to warrant jail time, but the local governments can be much lower, like just a few grams.
Virginia (my commonwealth) has a pretty low tolerance, any ammount can put you in jail.
"When the people find that they can vote themselves money, that will herald the end of the republic."- Benjamin Franklin