I have to agree. I followed the recommended link and took the data to the next level. To reproduce it here would a bit, so perhaps the simplest thing is to search on my user ID bpeterson272 and look at the plots.
Bottom line estimates are:
5-spd 31.0 highway / 23.3 city
CVT 29.5 highway / 23.5 city
5-speed manual transmission. The average mileage is a function only of the % city driving.
At 0% city driving the average driver should anticipate 31 mpg. 95% of all drivers should range between 26.4 – 35.6 mpg. This says only 2.5% drivers will achieve the EPA highway estimate or higher.
Each 10% increment of city driving will reduce the mileage 0.77 mpg.
At 100% city driving the average driver should anticipate 23.3 mpg.
CVT automatic transmission. The average mileage is a function of both % city driving and the total number of miles driven (rather interesting and unanticipated).
At 0% city driving and 0 miles on the car the average driver should anticipate 29.5 mpg. 95% of all drivers should range between 24.7 – 34.3 mpg. Only 0.15% of drivers will achieve the EPA highway estimate or higher.
Each 10% increment of city driving will reduce the mileage 0.60 mpg.
At 100% city driving the average driver should anticipate 23.5 mpg. For each 1000 miles driven the average fuel economy appears to increase 0.16 mpg up to 15000 miles where the data stops.
% city driving explains only 20% of the variation, leaving 80% to the "other" category. For the CVT, total miles driven explain another 10% of the variation, still leaving 70% in the "other" category. Not particularly impressive.
Lastly there is no observable break-in mileage change for the manual transmission.
There is a 1 mpg break-in for the CVT that shows up over time and takes about 7000 miles to develop. The data is sparse at higher miles driven so can't say if it flattens out or continues on for a while before it flattens out. My plots suggest it continues. I suppose the transmission has a period of time over which belt slippage is reduced although I imagine there are other explanations possible.