ABSTRACT
Let Y be a random variable dened as the “dependent” or “response” variable, and X another random variable dened as the “independent” or “factor” variable. Assume we have a joint sample xi, yi, i = 1, …, n or a set of n paired values of the two variables. This is a bivariate or two-variable situation. We already encountered this situation in Chapter 4 when we dened the covariance and correlation coefcient. Let us start this chapter by considering the scatter plot or diagram, which shows data pairs from a sample as markers on the x-y plane. As an example, Figure 6.1 shows pairs of x-y values for air temperature and ground-level ozone. Note that some pairs of points have much larger values of ozone concentration for the same temperature, as the trend would indicate. These are probably outliers and are identied by the observation number next to the marker.
