Use the applet. Go to the Correlation and Regression applet. Click on the scatterplot to create a group of 10 points in the lower-right corner of the scatterplot with a strong straight-line pattern (correlation about -0.9). In Exercise 4.48 (page 176) you started to see that correlation r is not resistant. Now click the "Show least-squares line" box to display the regression line.
(a) Add one point at the upper left that is far from the other 10 points but exactly on the regression line. Why does this outlier have no effect on the line even though it changes the correlation?
(b) Now move this last point down until it is opposite the group of 10 points. You see that one end of the least-squares line chases this single point, while the other end remains near the middle of the original group of 10. What makes the last point so influential?