Page "Regression toward the mean" Paragraph 25

The calculation and interpretation of “ improvement scores ” on standardized educational tests in Massachusetts probably provides another example of the regression fallacy.

In 1999, schools were given improvement goals.

For each school, the Department of Education tabulated the difference in the average score achieved by students in 1999 and in 2000.

It was quickly noted that most of the worst-performing schools had met their goals, which the Department of Education took as confirmation of the soundness of their policies.

However, it was also noted that many of the supposedly best schools in the Commonwealth, such as Brookline High School ( with 18 National Merit Scholarship finalists ) were declared to have failed.

As in many cases involving statistics and public policy, the issue is debated, but “ improvement scores ” were not announced in subsequent years and the findings appear to be a case of regression to the mean.