Always look at a scatterplot first

Although the correlation coefficient is a good description of the strength of many relationships, it does not adequately describe others.

A scatterplot should always be examined to help assess whether there are features in the data that the correlation coefficient cannot describe.

The data sets below share the same value of r = 0.816 (and the same means and st devns for X and Y) but their scatterplots show that different conclusions should be drawn from them.