A "Begin" button will appear on the left when the applet is finished loading. This may take a minute or two depending on the speed of your internet connection and computer. Please be patient. If no begin button appears, it is probably because your browser does not support Java 1.1.
Press the "Begin" button to start the applet in another window. The window opens contains with two identical scatterplots. The standard deviation of X is 10, the standard deviation of Y is 10, and the correlation between X and Y should be about 0.90.
For this demonstration, the reliabilities of X and Y are initially assumed to be perfect (1.0). The question is how decreasing the reliability of X and/or Y affects the regression analysis. You decrease the reliability of X by entering a positive number in the "sd of X error" field at the bottom of the window and clicking the "OK" button. This adds a random variable with a mean of 0 and the specific standard deviation to the variable X. This will decrease the reliability of X. For example, if the standard deviation of X's error is set to 10, then half the variance of X will be "real" and the other half will be error. This results in a reliability of 0.50. The reliability of Y can be changed in the same way.
This demonstration allows you to examine the effects of the reliability of X and Y on a number of the components of the regression analysis. Note that the results will differ slightly each time you click the "OK" button because the error variance is generated randomly.
The simulations were developed as part of a grant from NSF to David Lane of Rice University. Partial support for this work was provided by the National Science Foundation's Division of Undergraduate Education through grant DUE 9751307. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.