Simpson's paradox

Evidently, it has other names, but Simpson's paradox is a statistical phenomenon such that the combination of success rates is the reverse of the individual success rates. For example, in each of 1995, 1996, and 1997, David Justice had a better batting average than Derek Jeter. But the combined batting average of Derek Jeter was better than that of David Justice.

It happens when one part of the sample is out of proportion to the remainder of the sample. For example, if the two had similar batting averages over the three year period, except one year, David Justice had three at bats and reached twice. His batting average for the year would be .667, but it basically gets "lost in the wash".

Now I truly understand why they say that you can make statistics say anything you want.