How many hours of sleep per night does one need before there is a noticeable impairment in operating a vehicle?
Statistics can show whatever you want them to show.
My guess is is about 1%. Your second question needs to be reversed. Its not how much but how little. What you are trying to say is that a lot of accidents (60% or more) do not involve alcohol. And your third point is sort of true. So are you saying statistics have no value because of that or that we should be wary of how they are used? I think the 60 percent figure indicates driving in and of itself is a risky thing and alcohol doesn't exactly improve your odds any.