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

374 Educability and Group Differences
is 1 and for DZ twins (or full-sibs) is \ under random mating.
Under assortative mating pDZ will be greater than Theoretically,
a simplified but close approximation to pDZ under assortative
mating is given by
Poz =
(A.21)
2 + ppp
where ppp is the genetic correlation between the parents. It can be
estimated by h2rpp, where h2 is narrow heritability and rpp is the
phenotypic correlation between parents. A reasonable estimate of
pDZ based on obtained correlations between parental IQs is 0-55.
Other variance components can similarly be estimated from
differences between kinship correlations. For example, the proportion
of additive genetic variance, VA (which includes VAM),
is clearly approximated by rpd if VE is very small, as is usually
the case. Also, if V E is small, an estimate of the proportion of
VA is provided by the correlation of half-sibs reared apart, i.e.,
V J V p — 4th s a- This is also an estimate of the narrow heritability,
since h2 = VA/VP.
The proportion of dominance variance, VD, can be estimated
from the difference between the correlations of full-sibs reared
apart and twice the correlation of half-sibs reared apart, i.e.,
Equation A. 13 (substituting Equation A. 14 in the numerator)
minus 2 x Equation A. 15 ~ VDjV P. This assumes the same degree of
assortative mating for parents of full-sibs and parents of half-sibs.
The proportion of total environmental variance (including G x E
interaction and CovGE) is estimated by rtt —rMZA, where ru is the
test reliability (i.e., proportion of total variance minus error
variance). The proportion of between-families environmental
variance, VEg, plus interaction, VGE, and covariance, CovGE, are
estimated by rMZT —rMZA (i.e., Equation A. 10 —Equation A.ll).
The proportion of within-families environmental variance is, of
course, the total non-error variance minus the total betweenfamilies
genetic and environmental variance, or rtt—rMZT =
V b J V f.
Another way of estimating the between-families environmenta:
variance, VEg, is from the correlation between genetically unrelated
children reared together, rUT:
VE