Abstract: The regression toward the mean and other related characteristics in psychological testing were examined. The relations of reoccurrence probability of extreme scores to the distribution of true score, reliability, and the cutoff value of extreme scores are also scrutinized. Results showed that the regression toward the mean effect is larger when the reliability is lower or when the cutoff value is more extreme. For normally distributed data, the reoccurrence probability is related to reliability exponentially and to cutoff values linearly. Methods to avoid the regression toward the mean artifact are also generally discussed

Key words: testing, reliability, regression, regression toward the mean, extreme scores