An Improved Modification of a Regression-Toward-the-Mean Demonstration

Earlier simulations illustrating regression toward the mean have been improved so that they bear a closer resemblance to the actual phenomenon. In addition to the improved correspondence, the modified simulation permits a clear understanding of regression artifacts in two quasi-experimental designs, the extreme groups design and the matching-from-different-populations design. Highlighted in the simulation are: (1) the inverse relationship between measurement reliability (or between-measure correlations) and the magnitude of regression effects; (2) the stability of means and variances in the presence of regression effects; and (3) the time-reversed character of regression effects.