The following is an interesting paragraph from Matarazzo & Goldstein (1972):
Not sure if this says more about the relevance of grades or the validity of the original WAIS (at least at the high end).
No correlation between medical school grades & WAIS IQ?
14 Wednesday Aug 2024
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Pumpkin Person 
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Thanks for this very interesting tidbit. IQ certainly deserves the vast attention it has gotten from various researchers since Galton invented the field of intelligence research in 1869, but it bothers me that there as been such limited investigation of other factors that may contribute to achievement. I recall reading a footnote, I think in Frank Sulloway’s book “Born to Rebel,” that once you got above IQ 130, IQ was no longer predictive of one’s chance of winning a Nobel prize in science, which suggests that other factors are waiting to be identified. Jensen said that the IQ difference between the 20% most and least “successful” Termites was only 6 points.
Certainly some of the contributing factors are environmental, for example, Termites who “came of age” about the start of the Great Depression tended to have inferior outcomes to those who got started at better points in the economic cycle, but I strongly suspect there are inherited traits in addition to (and probably interacting with) g which also contribute to human achievement, and I really wish more researchers were interested in identifying these other factors. Once we have identified multiple factors that are likely to have an impact (and I have my own mental list of “suspects”), perhaps a regression analysis could be performed on all of them to provide some idea of each trait’s relative importance compared to the others. I do not understand why no one has attempted to do this yet, AFAIK.
I tend to think of intelligence as a turbocharger which supercharges other traits such as Conscientiousness, creativity (for which my favorite measure is the relatively recent and under-utilized ICAA, especially the Activities part), Epistemic Curiosity (or any of several highly correlated tests that measure essentially the same trait) or the general factor of spatial ability which explains the 0.80+ inter-correlations between multiple tests of spatial ability.
I think in Frank Sulloway’s book “Born to Rebel,” that once you got above IQ 130, IQ was no longer predictive of one’s chance of winning a Nobel prize in science,
I don’t know how he’d know that since so few Nobel prize winners have known IQ scores.
Jensen writes:
“One of the mistaken beliefs about the predictive validity of IQ (and other g loaded tests) is that beyond a certain threshold level, g has no practical validity,
and individuals who score at different levels above the threshold will be effectively equivalent in criterion performance. This is another way of saying that
the linear regression of the criterion on g does not hold above some point on
the scale of g and beyond this point g-level is irrelevant. This belief is probably
false. I have not found any study in which it has been demonstrated, except
where there is an artificial ceiling on the criterion measure.
This is not to deny that as variance in g is decreased (owing to restriction of
range in highly g-selected groups), other ability and personality factors that were
not initially selected may gain in relative importance. But studies have shown
that the linearity of the relation between g and performance criteria is maintained
throughout the full range of g for all but the least complex performance criteria.
Individual differences in IQ, even within groups in which all individuals are
above the ninety-ninth percentile (that is, IQ > 140), are significantly correlated
with differences in a variety of achievement criteria such as earning a college
degree, intellectual level of college attended, honors won, college GPA, attending graduate school, and intensity of involvement with math and science.
Since
these are statistical trends to which there are many exceptions, prediction based
on a g measure fo r a given individual is only probabilistic, with a wide margin
of error. When individuals of a given level of g are aggregated, however, and
there are several such aggregate groups, each at a different level of g, the correlation between the group means on g and the group means on the criterion
measure approaches unity. Since many idiosyncratic subject variables are
averaged out in the group means, the linear relationship of the criterion measure
to g is clearly revealed.”
The only part of the Jensen quote which is relevant to my comment is:
“…as variance in g is decreased (owing to restriction of
range in highly g-selected groups), other ability and personality factors that were
not initially selected may gain in relative importance.”
But even this probably does not go far enough. I remember seeing some data in one of Lynn’s books, I think it was his “Eugenics” book, that showed positive correlations between college grades and g and between college grades and Conscientiousness, but when both g and Conscientiousness were high, the achievement level was so much higher that it strongly suggests synergy.
Another example: Creative Abilities (as measured on the ICAA) and IQ are two normally distributed psychological metrics that are uncorrelated, but the Creative Achievement Questionnaire, a measure of creative achievements that were noteworthy enough to receive public recognition of some kind, is not normally distributed; instead most people score more or less nothing on the CAQ, and then you have a huge bubble at the right tail. This is explained by high scorers on the CAQ being elevated in both traits: IQ and (mundane) Creative Activities.
Another example is from college students with contrasting scores in spatial visualization. When IQ is the same or similar, spatial visualization scores (such as 3D figure rotation) predicts who majors in engineering or the hard sciences or math versus who majors in law or the humanities.
In a study of childhood prodigies, although all their prodigies were in the upper half of the IQ spectrum, their scores were otherwise all over the map and could not explain their prodigious accomplishments. However, every prodigy in that study had a working memory capacity in the top one percent.
Yes, I understand that IQ scores retain remarkable predictive power through the full extant range of scores, but it does not follow from that fact that they represent the sole heritable variable that explains differences in human achievement.
“Creative Abilities [sic] (as measured on the ICAA)” should read “Creative Activities,” not “Abilities.”