Regression to the Average

Regression to the Average provides still another way
to test if race differences are genetic. The children of very
tall parents are taller than average. But they are shorter
than their parents and nearer the average of their race.
Similarly, children of very short parents are shorter than
average, but taller than their parents. This is called the
Law of Regression to the Average. It is not true just for
height, but for IQ as well.   Most physical and
psychological traits show some regression effect.

Regression to the Average happens when very tall (or
very high IQ) people mate because they pass on some, but
not all, of their exceptional genes to their offspring. The
same thing happens with very short (or very low IQ)
people. It's like rolling a pair of dice and having them
come up two sixes or two ones. The odds are that on the
next roll, you'll get some value that is not as high (or as
low).

Here's why regression is important to our studies.
Because Whites and Blacks come from different races,
they have many different genes. The Law of Regression
predicts that for any trait, scores will return to the average
of their race. The Regression Law predicts that in the U.S.,
Black children with parents ofIQ115 will regress toward
the Black average of 85, while White children with parents
of IQ 115 will regress only toward the White average of
100.

The law also works at the other end of the scale. Black
children with parents of IQ 7Q will move up toward the
Black average IQ of 85, but White children with parents of
IQ 70 will move further up toward the White average of
100. When we test these predictions about Regression to
the Average from parent to child they prove true.

The Regression Law also works for brothers and
sisters. Black and White children matched for IQs of 120
have siblings who show different amounts of regression.
Black siblings regress toward an IQ of 85, while White
siblings regress only to 100. The opposite happens at the
lower end of the scale. Black and White children matched
for IQs of 70 have siblings who regress differently. Black
siblings regress toward an average of 85, whereas White
siblings move to 100.

Regression to the Average explains another interesting
finding. Black children born to rich parents have IQs that
are two to four points lower than do White children bom
to poor parents. The high IQ Black parents were not able
to pass on their IQ advantage to their children even though
they did give them good nutrition, good medical care, and
good schools. Only genes plus environment tell the whole
story.