After the rain-soaked debacle of the postponed MotoGP race at Qatar, any MotoGP fan worth his or her salt will be able to recite one statistic by heart: It only rains in Qatar for eight days a year, on average. And so staging a night race under the floodlights there, in the certain knowledge that the race must be canceled if it starts to rain, seems like a pretty safe bet. After all, 8 rain days out of a total of 365 means that there is only a 2.2% chance of the event having to be called off, right?
It seems like an obvious conclusion, but as with so many other conclusions drawn from statistics, it is completely incorrect. Human beings are notoriously bad at math, and this is just a typical instance. Just why this conclusion is incorrect is obvious when viewed logically, so let us look at it in more detail.
The key term to understand here is "average". It may well rain for 8 days a year on average, but that does not mean that those 8 days are spread evenly throughout the year - after all, the average temperature of the Earth is 14º Centigrade, or 57º Fahrenheit, but tell that to someone in Nuuk or Furnace Creek Ranch and they'll laugh in your face.