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.
Rainfall in Qatar is concentrated in the winter months - though the term "winter" should be taken in its loosest possible meaning. From June through October, rainfall average is zero, and May and November is little more. So those 8 days are not spread over 7 months, but rather 5, from December through April, more than doubling the probability of rain taken over the whole year. In fact, the records held by the World Meteorological Organization show that on average, Doha, the nearest large city, has 1.4 days of rain in April, or a probability of 4.6%, meaning it would rain on average once out of every 21 years on a given day in April.
But again, this too is not an accurate reflection. As the rain tails off towards the summer, it is more likely to rain at night in early April than it is in late April, further increasing the likelihood of rain. In fact, one travel site cites the average rainfall in Doha as between 2 and 6 days of rain a month between November and April, making the chances of rain on a given night in April even larger.
Even at the upper end of probability, the chances of it raining in Qatar are relatively slim - between 1 in 15 and 1 in 20. But given that there is a perfectly good solution for reducing the probability of having to cancel or postpone the race to almost zero - by running the race during the day, instead of under the floodlights - you have to wonder why Dorna would even risk running the race under the floodlights at all.