STATS ARTICLES 2010 Why any ol' diet will work (if your BMI is
high enough): A case study in regression toward the mean Rebecca
Goldin, PhD, February 10, 2010 Understanding regression toward
the mean Imagine a city where, from year to year, the overall
height of the population is stable. There are no sudden growth
spurts or frantic attempts by parents to give their children
growth hormones, or movements of very short people in or very
tall people out of the city limits. Now consider the following
statistical conundrum: if you measure the tall people in the
city, they will tend to have children who are shorter and,
similarly, the short people will tend to have children who are
taller. Other strange things are happening too. Though the
city's school test scores are not improving overall, the
children with the worst test scores last year, appear to be
doing better this year. What you are witnessing is called
"regression toward the mean," and it means that whenever you
measure something more than once in a popula