CRITIQUE OF The Bell Curve 373
Admittedly, factor analysis is a difficult and mathematical sub-
ject, but it can be explained to lay readers with a geometrical formu-
lation developed by L. L. Thurstone in the 1930s and used by me in
Chapter 7 of The Mismeasure of Man. A few paragraphs cannot suf-
fice for adequate explanation, so, although I offer some sketchy
hints below, readers should not question their own IQ's if the topic
still seems arcane.
In brief, a person's performances on various mental tests tend
to be positively correlated—that is, if you do well on one kind of test,
you tend to do well on the others. This result is scarcely surprising,
and is subject to either purely genetic (the innate thing in the head
that boosts all scores) or purely environmental interpretation (good
books and good childhood nutrition to enhance all performances).
Therefore, the positive correlations say nothing in themselves
about causes.
Charles Spearman used factor analysis to identify a single axis—
which he called g—that best identifies the common factor behind
positive correlations among the tests. But Thurstone later showed
that g could be made to disappear by simply rotating the factor axes
to different positions. In one rotation, Thurstone placed the axes
near the most widely separated of attributes among the tests—thus
giving rise to the theory of multiple intelligences (verbal, mathemati-
cal, spatial, etc., with no overarching g). This theory (the "radical"
view in Herrnstein and Murray's classification) has been supported
by many prominent psychometricians, including J. P. Guilford in
the 1950s, and most prominently today by Howard Gardner. In this
perspective, g cannot have inherent reality, for g emerges in one
form of mathematical representation for correlations among tests,
and disappears (or at least greatly attenuates) in other forms that
are entirely equivalent in amounts of information explained. In any
case, one can't grasp the issue at all without a clear exposition of
factor analysis—and The Bell Curve cops out completely on this cen-
tral concept.
On Kaus's second theme of "cultural bias," The Bell Curve's pre-
sentation matches Arthur Jensen's, and that of other hereditarians,
in confusing a technical (and proper) meaning of bias (I call it "S-
bias" for "statistical") with the entirely different vernacular concept
(I call it "V-bias") that agitates popular debate. All these authors
swear up and down (and I agree with them completely) that the tests