EXAMPLE 1.28 Fuel Efficiency

Figure 1.17 is a histogram of the fuel efficiency, expressed as miles per gallon (MPG), for highway driving, for 1067 motor vehicles (2014 model year) reported by Natural Resources Canada.²⁵ Superimposed on the histogram is a density curve. The histogram shows that there are a few vehicles with very good fuel efficiency. These are high outliers in the distribution. The distribution is somewhat skewed to the right, reflecting the successful attempts of the auto industry to produce high-fuel-efficiency vehicles. The center of the distribution is about 38 MPG. There is a single peak, and both tails fall off quite smoothly. The density curve in Figure 1.17 fits the distribution described by the histogram fairly well.