Consider Table 1, which contains measurements on two variables for ten people: the number of months the person has owned an exercise machine and the number of hours the person spent exercising in the past week.
If you display these data pairs as points in a scatter plot (see Figure 1), you can see a definite trend. The points appear to form a line that slants from the upper left to the lower right. As you move along that line from left to right, the values on the vertical axis (hours of exercise) get smaller, while the values on the horizontal axis (months owned) get larger. Another way to express this is to say that the two variables are inversely related: The more months the machine was owned, the less the person tended to exercise.
Figure 1. The data in Table 1 is an example of negative correlation.