Follow the money. The professional 'substance abuse' experts love this stuff.
Joe Blow gets in an auto accident and has to be taken to the hospital. The cops find a 2 month old roach in his ashtray and suddenly the accident is 'drug related'.
The professional victim makers (i.e. treatment centers) get the next INVOLUNTARY referral.
Oh yeah, and poor ol' Joe loses his license to boot.
Ol' Joe walks down to the river to go fishing. He slips and falls causing a visit to the emergency room. The staff question him about his entire chemical using history and he admits that he has smoked weed before.
Ding. ding. ding. New referral for the treatment center and another 'drug related' accident for the stats.
You don't know how true that is. Four years ago, a friend of mine had his car broken into when he was parked downtown. He had one tiny roach in his ashtray that had probably been there two weeks (not smart to leave that in the car, but beside the point).
The officer who wrote up the break in report found the roach. He wasn't that gung ho about about busting my friend for the roach, but said he had to note it in the report "for statistics purposes". I asked him what that meant. He rolled his eyes and said anytime a crime is committed and there's any signs of drugs in the periphery, they're required to make note of it.
"So this will be classified as a drug-related crime?", I asked him. "Yep", he said. I asked if that made any sense to him and he replied, "Not at all, but I don't make the rules."
After that, I've been 100% skeptical about drug-related statistics. It's all too easy for the fedgov to artificially inflate the numbers.
I suppose if I run a red light and the cops find rolling papers in the periphery (which is what... 100 feet... 1 mile?), that would also be a drug-related crime even though I've never used a drug in my life.