Friday, November 20, 2009

If you aren't cheating, you aren't trying: the importance of Cherry Picking.

Cherry picking is the often-derided term for picking out a limited supply of points, and then trying to prove a point from them.
But Cherry picking isn't always a bad thing, as long as you remember that its main use is for DISPROOF, not PROOF.
If I pick out two points that have a counter-intuitive result, it means that the intuitive result can not be totally true!
And, to illustrate, an example:This diagram shows the connection between a city's size and the percentage of its population that is African-American. African-Americans typically do live in larger cities, but as this diagram shows, there are at least some exceptions to this rule. Fairbanks, Alaska, a town of around 30,000 people, has the same percentage of African-Americans as Los Angeles, a town 100 times its size. And a higher percentage than some much larger towns.
Now, of course if I put more data points into this, it would probably have a line closer to what we expect. But as long as Fairbanks is there, the plot will never be perfect!

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