Educability-and-Group-Differences-1973-by-Arthur-Robert-Jensen

Appendix on Heritability 369
The distinction between the h2 as defined by Equations A.5
and A.6 is seldom made explicit in the literature and depends upon
the method used for estimating h2. Generally, CowGE is included
in h2 (i.e., formula A.6), either on the assumption that the covariance
is due to the genotype and/or because the particular method
of estimating h2 does not permit separation of VGand Co vGE.
BETWEEN- AND W ITHIN-FAM ILY COMPONENTS
For reasons that will become apparent in the following section, it
is useful to partition both the genetic variance, VG, and the
environmental variance, VE, each into two components, one due
to differences between families and one due to differences within
families:
Vg = VGb + VGw
where
VGg = genetic variance between families
Vq = genetic variance within families.
(A.7)
This formula reflects the fact that there are genetic differences
between the average value of the trait measurement of different
families in the population and also genetic differences among the
offsprings within each family.
Ve = VEb + VEw (A. 8)
where
VF = environmental variance between families
3
V F = environmental variance within families.
Formula A.8 reflects the idea that there are systematic environmental
differences between families which make for differences
between families on the trait in question but do not make for
differences among offsprings reared together in the same family;
this is Vr
B
. And there are differential environmental influences
within families which make for differences among offsprings reared
together in the same family; this is VEw. These environmental
effects, VEb and VEw, can occur at any time after the moment of
conception; some are prenatal, some are postnatal; some are
associated with biological factors, such as nutrition and disease;
some are psychological, social, and cultural.