A COMPUTER-PROGRAM THAT DEMONSTRATES THE DIFFERENCE BETWEEN MAIN EFFECTS AND INTERACTIONS

This article describes a QuickBASIC program for demonstrating the diff erence between main effects and interactions in factorial designs. The program guides the student through the construction of data patterns corresponding to different combinations of the main effects and the in teraction in a 2 x 2 design. Program feedback provides tailored guidan ce to help students produce the requested patterns of means. The progr am also generates ideal solutions for comparison. To simulate actual e xperience, the program generates a data set (N = 80) for each construc ted pattern of means and calculates the rests of significance for the main effects and interaction. The program can be used in conjunction w ith a traditional lecture on factorial designs to improve student unde rstanding of main effects and interactions and to develop student skil l in recognizing main effects and interactions from graphical displays .