Regression to the Mean

Regression to the mean can be defined as the changes that take place over time among exceptional individuals and groups, and across generations they tend to be toward the average for the larger population from which they are drawn. Many of the changes observed emerge from the fact that the measurements involved are composed of two parts: (1) a valid part and (2) a random error part. In much of the medical and healthcare research, extreme values on the first test or measurement are likely due in part to the random error component. By chance alone, that random error component is likely to contribute less on the next measurement.