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

Environmental Rationalization v. Research 233
which could cause them to question the null hypothesis regarding
genetic differences, or even to reject a particular environmental
factor which has been postulated as a cause of IQ differences
Various environmental factors are constantly repeated in the environmentalist
literature as a cause of IQ differences, even when
studies specifically designed to test these hypotheses have yielded
largely negative results. There seems to be no way for the environmentalist
to give up any hypothesized environmental factor;
regardless of the outcomes of empirical tests, each newly hypothesized
factor is added to the growing list of purported environmental
causes of IQ differences.
The principal environmentalist fallacy consists of looking for any
environmental differences that exist between two subpopulation
groups which differ in mean IQ and merely assuming that the
environmental differences are the cause of the IQ difference;
usually it is not even regarded as necessary to demonstrate that
a non-zero correlation between the hypothesized environmental
factor and IQ exists within the groups. At least three critical
questions need to be answered about every hypothesized environmental
factor before one can even begin to consider whether it is
a causal factor: (1) Does it correlate with the trait in question within
the two groups being compared (2) How much do the groups differ
on the environmental factors (3) Does the factor make any
significant contribution to within-groups or between-groups variance
in the trait independently of other hypothesized factors As
pointed out in a previous section, one cannot properly assess the
importance of a large number of intercorrelated environmental
factors from the single (zero order) correlations of each one with
IQ. It is each variable’s independent contribution to the multiple
correlation that counts. When major environmental factors fail to
account for IQ differences sufficiently to sustain the environmental
hypothesis, other subtler environmental factors are then postulated,
and they may be tested in a new study and be found to show some
correlation with the IQ difference. But rarely are they combined
with the variables of the first study to see if they in fact add any
significant increment to the coefficient of multiple determination
(R2). Even if they do, the direction of the causality often remains
an open question which can be answered only by evidence other
than correlational data. The pattern of multiple correlations at
best narrows the range of possibilities in seeking the most