Simpson's Paradox

The 12th principal, according to Dr. Bracey, states: "Watch out for Simpson's Paradox." I further researched Simpson's Paradox:

The Simpson's Paradox was first discovered by Karl Pearson (1899) and Undy Yule (1903), but further elaborated by Edward H. Simpson (1951), and again by Colin R. Blyth (1972).

There are at least three variables related to Simpson's Paradox:
1. the explained
2. the observed explanitory
3. the lurking explanitory

For a more in depth explanations follow these links:
http://vudlab.com/simpsons/
http://en.wikipedia.org/wiki/Simpson%27s_paradox