EXAMPLE 2.3 Spending and population

CASE 2.1 A state with a larger number of people needs to spend more money on education. Therefore, we think of population as an explanatory variable and spending on education as a response variable. We begin our study of this relationship with a graphical display of the two variables.

Figure 2.1 is a scatterplot that displays the relationship between the response variable, spending, and the explanatory variable, population. The data appear to cluster around a line with relatively small variation about this pattern. The relationship is positive: states with larger populations generally spend more on education than states with smaller populations. There are three or four states that are somewhat extreme in both population and spending on education, but their values still appear to be consistent with the overall pattern.