Because IQ scores, like almost all dependent variables, are influenced by random and systematic factors, these scores are subject to

regression to the mean.

Regression to the mean is that things are never as bad or as good as they seem.

Given the

regression to the mean present in the cross-national data, however, where growth rates historically have averaged 2 percent with a standard deviation of 2 percent, the authors conclude that continued rapid growth would be an extraordinary event.

In addition, we made use of two years of cost and utilization data prior to program implementation, and thus addressed possible

regression to the mean effects.

Regression to the mean suggests that extreme observations (in either direction) will eventually move toward the mean (Galton 1886), particularly if the observations are extreme due to measurement error (Cook and Campbell 1979).

Regression to the mean refers to the idea that schools above or below the mean--likely move toward file mean simply because that is the only direction those schools can go.

The advantage of practicing personalized methods is obvious when we consider that the phenomenon of

regression to the mean is more pronounced for participants in this program.

Their topics include mathematical coupling and

regression to the mean in the relation between change and initial value, collinearity and multicollinearity, and finding growth trajectories in lifecourse research.

In addition, we will consider a third comparison, where we will build a comparable dataset to estimate the expected

regression to the mean and to see if a similar effect can be found in a dataset where the actual participation in the Derby is not present as a variable.

One might contend that the improvement observed after the initial administration of the feedback program is due to

regression to the mean.

Second, the report's reliance on state assessment data is misleading, and some schools' reported growth may be an artifact of

regression to the mean and ceiling effects as well as instructional and testing practices.

If the random error in this variable is an appreciable proportion of between subject differences (that is, the variable has moderate to low reliability), the baseline values have a substantial artifactual negative correlation with the change scores known as

regression to the mean.