‘Most of you will have heard the maxim “Correlation does not imply
causation.” Just because two variables have a statistical relationship with
each other does not mean that one is responsible for the other. For
instance, ice cream sales and forest fires are correlated because both occur
more often in the summer heat. But there is no causation; you don’t set a
patch of the Montana brush on fire when you buy a pint of Häagen-Dazs.’
Nate Silver