Looking at my 7+ years consumption figures in more detail, I find that for the 4 years when we lived 4 miles out of town and also had a Yaris which was used mainly by my wife for local trips, the Jazz averaged 48.4 mpg. We then moved into the centre of town and sold the Yaris, since when the average Jazz consumption has changed to 46.1 mpg. I'm not suggesting for a moment that my wife has a heavier right foot, but simply that the journey mix has changed, with the Jazz doing more short runs since we moved. This shows how difficult it is to do meaningful comparisons.