Importance
Regression toward the mean is a significant consideration in the design of experiments.
Take a hypothetical example of 1,000 individuals of a similar age who were examined and scored on the risk of experiencing a heart attack. Statistics could be used to measure the success of an intervention on the 50 who were rated at the greatest risk. The intervention could be a change in diet, exercise, or a drug treatment. Even if the interventions are worthless, the test group would be expected to show an improvement on their next physical exam, because of regression toward the mean. The best way to combat this effect is to divide the group randomly into a treatment group that receives the treatment, and a control group that does not. The treatment would then be judged effective only if the treatment group improves more than the control group.
Alternatively, a group of disadvantaged children could be tested to identify the ones with most college potential. The top 1% could be identified and supplied with special enrichment courses, tutoring, counseling and computers. Even if the program is effective, their average scores may well be less when the test is repeated a year later. However, in these circumstances it may be considered unfair to have a control group of disadvantaged children whose special needs are ignored. A mathematical calculation for shrinkage can adjust for this effect, although it will not be as reliable as the control group method (see also Stein's example.)
The effect can also be exploited for general inference and estimation. The hottest place in the country today is more likely to be cooler tomorrow than hotter, as compared to today. The best performing mutual fund over the last three years is more likely to see relative performance decline than improve over the next three years. The most successful Hollywood actor of this year is likely to have less gross than more gross for his or her next movie. The baseball player with the greatest batting average by the All-Star break is more likely to have a lower average than a higher average over the second half of the season.
Read more about this topic: Regression Toward The Mean
Famous quotes containing the word importance:
“There are of course people who are more important than others in that they have more importance in the world but this is not essential and it ceases to be. I have no sense of difference in this respect because every human being comprises the combination form.”
—Gertrude Stein (1874–1946)
“Kitsch is the daily art of our time, as the vase or the hymn was for earlier generations. For the sensibility it has that arbitrariness and importance which works take on when they are no longer noticeable elements of the environment. In America kitsch is Nature. The Rocky Mountains have resembled fake art for a century.”
—Harold Rosenberg (1906–1978)
“The chimney is to some extent an independent structure, standing on the ground, and rising through the house to the heavens; even after the house is burned it still stands sometimes, and its importance and independence are apparent.”
—Henry David Thoreau (1817–1862)