There’s no reliable way to determine impairment from a blood test. At most, this says that ~42% of people used it recently and/or frequently enough for metabolites to be present.

https://forensicresources.org/2021/marijuana-impairment-faq/

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jeremyjh a day ago | parent [-]

Sure, but if the baseline level of annual usage is only 20% in the general population then you still have a significant correlation.

	▲	Ancapistani 3 hours ago \| parent [-]
		Correlation, and about a billion compounding factors. For example: younger people are more likely to be regular cannabis users - and are also more likely than the general public to get in motor vehicle accidents.