Friday, January 21, 2005

How not to collect statistics

An annual report on illicit drug use in Toronto has found a significant number of young people admit to smoking marijuana and driving.

The report was compiled by 20 agencies, including the Centre for Addiction and Mental Health, the Toronto Police and Toronto Public Health.

It says that 14 per cent of of students in Grades 10 to 12 admit to driving an hour after using marijuana.


Question: why were they including Grade 10 students in the poll? Grade 10 is for people who turn 15 by the end of December. That means that, with the exception of students who skip a year or a held back a year, the youngest Grade 10 students (in September) are about 14 years and 8 months old, and the oldest Grade 10 students (in June) are about 16 years and 6 months old.

In Ontario, you can get a G1 (learner's) licence on your 16th birthday, but you can't drive without an accompanying adult until you've had your G1 for at least 8 months. This means that the vast majority of Grade 10 students aren't even old enough to drive by themselves. If you're doing a poll about driving habits, why would you include a significant number of people who have no possible way to be legally allowed to drive?

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