For Exercises 2.1 and 2.2, pages 64–65; for 2.3 and 2.4, see page 65; for 2.5 and 2.6, pages 66–67; and for 2.7, see page 68.
2.21 Fuel efficiency and CO2 emissions
canfuel
Refer to Example 2.7 (pages 70–71), where we examined the relationship between CO2 emissions and highway MPG for 1067 vehicles for the model year 2014. In that example, we used MPG as the explanatory variable and CO2 as the response variable. Let's see if the relationship differs if we change our measure of fuel efficiency from highway MPG to city MPG. Make a scatterplot of the fuel efficiency for city driving, city MPG, versus CO2 emissions. Write a summary describing the relationship between these two variables. Compare your summary with what we found in Example 2.7.
2.21
There is a negative relationship between City MPG and CO2 emissions; better City MPG is associated with lower CO2 emissions. The relationship, however, is not linear but curved. There also seems to be two distinct lines or groups. This relationship is very similar to what we found in Example 2.7 when using highway MPG, with the patterns seen in the plot nearly identical to the form we saw in Example 2.7.