Internet Exercises

This exercise provides an excellent opportunity to see how explained variance differs depending on slope and dispersion of scores. After reading the directions, click "Begin" and the applet will appear on the screen. Click on "Animate slope" and watch how the explained and unexplained variance bars (on the right side of the screen) change as the degree of slope changes. Also, examine changes that happen to both the correlation coefficient and standard deviation. Stop the animation of slope at 1.00 and click on "Animate SE." Note the changes to both the explained standard deviation and variance. End the exercise by clicking "Animate sd of X." Pay careful attention to the appearance of data when error increases. Use your observations from this exercise to explain the pattern of data when error is high. Also, discuss the slope on the scatterplot relative to error.

In this exercise you see the change in the regression line when a single outlier is added to the scatterplot. When the window opens, note the values in the y equation (y = 2.946 + .9796x; r - .998). Use the mouse to move the cursor to a point just above the 100 score on the x-axis and click. Notice this adds an added value to the scatterplot. What is the impact of the added value, an extreme score, to the regression line?