These are based on data from a household survey, which did not exactly ask the people if they'd been driving drunk or anything. This is not how it's being addressed. The question would be as follows, “In the past 12 months, have you driven a motor vehicle under the influence of an illicit substance such as marijuana or hashish?” That would be for the drug-impaired driving. In the case of alcohol, we would ask them if they had done so after consuming two drinks in the hour preceding their departure.
We cannot conclude necessarily that these were impaired drivers. That would vary a lot depending on their constitution and how they are built and everything, but we were able to make some associations between those behaviours, if they were repeated behaviours, because we were asking if they did it often or just once.