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

308 Educability and Group Differences
at the top.3 That is to say, for any value of G, the value of P for
group A will exceed that of group B by 1 SD. (The dots represent
the bivariate means of groups A and B and the solid and dashed
lines are the regression of P on G or G on P.)
Hypothesis 2 is a strictly genetic hypothesis; the groups differ in
genotype but not in environment (GA>GB and EA= EB). Here
we see that the regression of P on G (and G on P) is the same
line for both groups.
Hypothesis 3 is a combined genetic and environmental hypothesis,
with two parts: (i) group A is more advantaged than group B
both genetically and environmentally (GA>GB and EA>EB), and
(ii) the genetic difference is greater than the environmental
difference {GA—GB>EA—EB). Note that in this case the regression
line PA is above Pb, as in the top left graph (Hypothesis 1),
but unlike Hypothesis 1, in Hypothesis 3 the regression line GA
remains above GB.
Now, with the consequences that logically follow from these
three clearly formulated hypotheses made explicit, as shown in
the regression lines of Figure 17.3, we can perform an empirical
test of these hypotheses. Naturally, we can only crudely approximate
the idealized hypothetical regressions shown in these graphs
since there are no perfectly culture-free tests, i.e., tests with
h2 = 1-00. The best we can do at present is to use two tests which
differ most conspicuously in culture-loading. (The most cultureloaded
test corresponds to P in Figure 17.3 and the least cultureloaded
test corresponds to G.) For this purpose we have chosen
Raven’s Matrices and the Peabody Picture Vocabulary Test
(PPVT). We have already pointed out that the Raven is one of the
most culture-reduced tests available. The PPVT provides a
striking contrast. It is probably the most culture-loaded among
all standardized IQ tests currently in use. The test consists of
150 plates each containing four pictures. The examiner says a
word that labels one of the four pictures in each set and the testee
is asked to point to the appropriate picture. The items increase
in difficulty by increasing the rarity of the pictured objects and
their corresponding verbal labels. Figure 17.4 shows the mean
frequency of these words per every million words of printed
English in American books, magazines, and papers. It can be
seen that for both equivalent forms of the test (A and B), the
commonness of the words decreases systematically from the first.