Statistical regression or regression to the mean. Statistically, extreme scores on an original test will tend to become less extreme upon retesting. Example: Hank was tested in the vocational...

Statistical regression or regression to the mean. Statistically, extreme scores on an original test will tend to become less extreme upon retesting. Example: Hank was tested in the vocational rehabilitation office and received one of the lowest scores ever recorded there, a fact that attracted some attention from the counselors who worked with him. However, because of a bus strike, Hank couldn’t get to the center very often, and yet, upon retesting, he scored much better than he had before. Had Hank been receiving counseling during that period, it might have appeared as though the counseling produced the changes in score.