1. Select Correlation Demonstration from the main menu.
2. Press a number key from 1 to 9, to interchange that number of data pairs (you can do this as often as you like in each demonstration).
The computer will initially present you with a scatterplot of a nearly perfect, positive correlation of 26 pairs of data. The best fitting regression line is drawn through the pairs. When you press a number key between 1 and 9, the computer will randomly interchange that many data pairs, and the resulting correlation and regression line will change.
The purpose of the Correlation Demonstration is to give you experience with lots of scatterplots, ranging from those that depict nearly perfect correlations to those that (by interchanging data pairs) depict nearly zero correlations.
The Effect of Interchanging One or More Data Pairs
Start the Correlation Demonstration and press the number key 1 to interchange one pair of data points. You will see that just interchanging one data pair can have a dramatic effect on the correlation. Alternatively, you can choose to interchange one or more pairs of data points for the same scatterplot, (press 1, then 1 again, and so on). This has the effect of changing the value of the correlation each time you press 1. For a high (absolute) correlation the value will usually decrease.