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:
- Assume one-sixth of the 08 cars were sold in March 2008 (an underestimate);
- Assume a ratio of 1:20 for 09:08 plates (an approximation, but not a bad one);
- This means that there were roughly one-third as many 09 cars registered last month as in last March.