Wednesday, 8 April 2009

Recession or not? Judge for yourself

The motor trade claimed that car sales last month were down by 30%. My, statistically unsound, survey suggests that it is probably down by more like 70%.

How did I carry out my survey?

Well my son and I were driving down the motorway yesterday, and he was getting bored. So, what we did was counted 08 car registration plates, and kept counting them until we saw a 09 plate. The average count was over twenty cars with 08 plates before seeing an 09 plate. Try it yourself.

Now for the maths...

Please note this is a simplified approach - if you want the full version email me, but it involves some fairly complex stats:
  1. Assume one-sixth of the 08 cars were sold in March 2008 (an underestimate);
  2. Assume a ratio of 1:20 for 09:08 plates (an approximation, but not a bad one);
  3. This means that there were roughly one-third as many 09 cars registered last month as in last March.
So how can the industry claim only a 30% fall? My guess is that they are pre-registering a huge number of cars and then leaving them in stock.

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