Regression toward the mean is a statistical phenomenon in which extreme scores collected at one time point tend to be closer to the mean of the data set when collected again at a another time point (i.e., they regress to the mean), even without any intervention. In other words, a score that is extreme in one measurement is likely to be not so extreme (i.e., closer to average) at a different point of measurement. This phenomenon requires acknowledging that chance factors (i.e., noise, random error) are part of most measurements; that is, any measurement is likely a combination of truly valid data and fluctuating factors. Regression toward the mean represents a known statistical fact that things that are subject to chance factors tend to even ...