Simpson’s Paradox
In 1995, as well as in 1996 baseball player David Justice had a higher Batting Average than Derek Jeter (0.253 vs 0.250, and 0.321 vs 0.314). But, combining the statistics of both years to a single aggregate number will show Derek Jeter as the clearly better hitter (0.310 vs 0.270). Weird, isn’t it?
Read more at Wikipedia: http://en.wikipedia.org/wiki/Simpson’s_paradox
