powerful impact on r and may cause us to overinterpret the relationship. You must look at the
scatterplot of the data as well as r .
example: To illustrate that r is not resistant, consider the following two graphs. The graph on the
left, with 12 points, has a marked negative linear association between x and y . The graph on
the right has the same basic visual pattern but, as you can see, the addition of the one outlier has
a dramatic effect on r —making what is generally a negative association between two
variables appear to have a moderate, positive association.example: The following computer output, again for the hours studied versus exam score data,
indicates R-sq, which is the square of r . Accordingly, There is a lot of
other stuff in the box that doesn’t concern us just yet. We will learn about other important parts
of the output as we proceed through the rest of this book. Note that we cannot determine the
sign of r from R-sq. We need additional information.(“R-sq” is called the “coefficient of determination” and has a lot of meaning in its own right in
regression. It is difficult to show that R-sq is actually the square of r . We will consider the
coefficient of determination later in this chapter.)Calculator Tip: In order to find r on your calculator, you will first need to change a setting from the