Why does the bar graph for all cars in a specific car type not match up with the listing of individual cars and their mpg? For example, for the Honda Insight, I counted nine cars averaging 49.0 - 49.9 mpg. However, the bar graph for Insights shows only 2 cars averaging 49 mpg. Even if you round up/down, the figures still don't match up. How is the data for the bar graphs calculated?
It's not quite a standard round up/down, and that might be where the confusion is. Technically, we're using a ceiling function on all averages to create the graph. That allows us to plot full integers.
So in your example (as I look at the Honda Insight page now), the graph says there are 3 at 49 and 8 at 50. So I think you're just seeing an odd spot in the data where there's a jump between integers. I know it's confusing to see so many 49.x's in the mix, but those are being counted as 50s.