The average mpg bar graphs for a car model are misleading, due to the discontinuous nature of the classes. As an example, if you go to
http://www.fuelly.com/car/ford/fiesta you will see what appears to be a straightforward distribution of mpgs. If you look to the right hand side of the graph, you see that the range is discontinuous, going 47,48,51,52,58.
This is because bars are only drawn if you have 2 or more values in that category. However, this is very misleading. What is worse, if you filter on Diesel L4, you can see that there are also entries for 56,61,62,64 and 66 with a further 60 under Diesel H4 and a 67 under Diesel (no specification).
So, the graph totally obscures the fact that there is skewed distribution. The problems this can result in is very clear when you select the 2010 Fiestas. This looks like a continuous distribution, but there is a huge gap in the middle, and it is actually two separate distributions, due to the difference between Petrol and Diesel fuel economies. This graph is simply misleading.
By all means adjust the classes to deal with low numbers (ie graph 41-45, 46-50, 51-55) but the graphs should have equal class sizes, and should include all values.
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