July 20th, 2004

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Meaningless Numbers

There are three types of lies: lies, damn lies, and statistics. -- Samuel Clemens, A.K.A. Mark Twain

From http://story.news.yahoo.com/news?tmpl=story&cid=572&e=14&u=/nm/health_marijuana_dc

"And it found the age of youths using marijuana is falling. The teens aged 12 to 17 said on average they started trying marijuana at 13-1/2. The same survey found that adults aged 18 to 25 had first tried it at 16."

Does anybody else see what's wrong with this number?

Here's the thing: It's comparing a difference between two distinct populations, when that which decides between populations is numerically related to the difference.

Think about this. If you're polling those in the age range of 12 to 17, it will be impossible to get a value of 18 or higher. All numbers will fall in the range from zero to 18.

Polling adults? The range is now zero to 25. So, perhaps, the exact same data point count could be plotted over the curve of those who answered in the 12 to 17 poll- but then there are the additional possible values, pulling the number to the older. The number given is completely meaningless.

Great reporting, Yahoo.
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