A famous slogan in statistics is that correlation does not imply causation. We know that there is a statistical correlation between eating ice cream and drowning incidents, for instance, but ice cream consumption does not cause drowning. Where any two factors – A and B – are correlated, there are four possibilities: 1. A is a cause of B, 2. B is a cause of A, 3. the correlation is pure coincidence and 4., as in the ice cream case, A and B are connected by a common cause. Increased ice cream consumption and drowning rates both have a common cause in warm summer weather.