Thursday, February 6, 2014

That Many, Really?

The Minnesota Department of Public Safety released news that 12% (1 in 8) of vehicle operators are driving illegally with no license, revoked or suspended licenses, etc. This seems really alarming. Other studies have shown rates close to 1 in 12 (8%) to 1 in 5 (20%).

Before we start suspecting the drivers in front, behind and beside us as immoral schlumps, we need to realize the source of this data. It's taken from criminal records--tickets, court cases, and the like. The information we can cull from this has an inherent bias.

It's not a randomly selected sample of drivers. That would be more telling of the true nature of the problem. All we know is that those who drive poorly have a significant rate driving illegally. Those who don't have accidents or don't get caught in other traffic violations may or may not be more likely to drive without a valid license. The assumption behind these reports is that the proportion of problems is the same in the whole population as it is in the biased sample. Not a good assumption.

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