One indication that Spearman's g (upon which IQ is based) is an artifact of positive correlations among various intelligence test measures than a real thing is that there are subpopulations among which these measures do not correlate in the same way as among the general public.
An example is here: (note, my interpretation of their findings):
To quote:
An example is here: (note, my interpretation of their findings):
Psychol Sci. Author manuscript; available in PMC 2015 Jan 8.Published in final edited form as:PMCID: PMC4287210NIHMSID: NIHMS653064The Level and Nature of Autistic Intelligence
To quote:
For example, no autistic child scored in the “high intelligence” range on the WISC-III, whereas a third of the autistic children scored at or above the 90th percentile on the Raven’s Matrices. Only a minority of the autistic children scored in the “average intelligence” range or higher on the WISC-III, whereas the majority scored at or above the 50th percentile on the Raven’s Matrices. Whereas a third of the autistic children would be called “low functioning” (i.e., in the range of mental retardation) according to the WISC-III, only 5% would be so judged according to the Raven’s Matrices.
In striking contrast to the autistic children, the nonautistic control children did not show a significant difference between their Raven’s Matrices scores and their WISC-III Full Scale, Verbal Scale, or Performance Scale scores .So, if there was a real thing X corresponding to Spearman's g that represented the intelligence of a human brain, then the general positive correlation in the general population between WISC and Raven's Matrices is not measuring this thing X. But it is these kinds of positive correlations among the various tests' results that is supposed to be measuring this real thing that is approximated by Spearman's g.
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guest · 387 weeks ago
Genetic correlation studies suggest that whatever it is that IQ tests measure is governed by a very large number of genes, meaning that there must be many partially independent factors involved in IQ.
Nonetheless, g is not a myth but a statistical fact. The fact that these correlations exist has been repeatedly demonstrated, and exceptions, while interesting and possibly informative don't disprove them any more than throwing three heads in a row disproves statistics. The fact that such correlations exist in the face of both a multifactorial origin and inevitable exceptions is surprising, but it's a durable statistical fact.
guest · 387 weeks ago
The oddity is that the "real thing" being measured almost certainly cannot be a unitary genetic factor, since genetic analyses should have pinpointed it. Another old theory is that low IQ is due to various specific genetic or developmental defects. This one has some confirming examples. In that case, high IQ might simply mean having relatively few such defects.