This reminds me of the story of how Target were able to quite precisely figure out whether their female customers were pregnant, and even when the due dates were: <a href="http://www.nytimes.com/2012/02/19/magazine/shopping-habits.html?pagewanted=all" rel="nofollow">http://www.nytimes.com/2012/02/19/magazine/shopping-habits.h...</a>