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I am roommates with a maxillofacial surgeon. He told me that during his studies he read that cephalic index can be used to measure intelligence.

And he further explained that as Africans and women have smaller brains according to cephalic index, so they are less intelligent than Caucasian and Asian men.

I just want to know how much of this is true, if any? And please explain.

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    $\begingroup$ There is also no clear understanding what intelligence is or how to measure it effectively. With no way to adequately measure intelligence, it seems rather doubtful that any linear statistical relationship could be developed with anything else. $\endgroup$ – user104078 Nov 5 '17 at 21:55
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No, the index and its correlation to intelligence is not strong.

See the medchrome.com description on cephalic index:

  • The underlying assumption of craniometry is that skull size and shape determine brain size which determines such things as intelligence and capacity for moral behavior. Empirical evidence for this assumption is not very strong.
  • Cephalic index consistently produced a very low or negative correlation with mental ability.

See also this article on Smithsonian.com: Why Brain Size Doesn’t Correlate With Intelligence

Healy and Rowe (2007) provide a critique of comparative studies of brain size.

Healy, S. D., & Rowe, C. (2007). A critique of comparative studies of brain size. Proceedings of the Royal Society of London B: Biological Sciences, 274(1609), 453-464.

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(It wouldn't let me just comment) I would add, there are multiple cases where the apparent size of the skull and therefore brain do not correlate with intelligence, and this is across different species of the planet. If it were true, why are humans one of the apparently most intellectually evolved creatures? Consider whales. This cannot be explained by the aforementioned method. If one were to look at brain size in the human population they appear to actually be decreasing in size over time, which could lead one to conjecture people aren't getting less intelligent but that the density of neurons is changing. The density is increasing. We can justify the lack of decreasing intelligence by the intelligence metrics that exist today, regardless of how flawed they may actually be, they show an average increase compared with the past. So, in the human case, if you were take density into consideration then this altogether and at once dismisses the idea you speak of as being patently false.

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