Cranial Size and Intelligence Link

In summary, the conversation revolves around the correlation between cranial size and intelligence. Some individuals argue that there is a clear link between the two, citing numerous studies published in mainstream journals. Others question the validity of this correlation, pointing out that the correlation coefficients found in these studies are not strong enough to support a direct relationship. There is also a discussion about other factors that may influence this correlation, such as income and general quality of life. However, there is no clear consensus on the matter and the conversation ends with a request for further explanation.
  • #1
BlackVision
28
1
Even though I and others have expressed that there was nothing wrong with the original "Cranial Sizes Between Races" thread as it was completely scientific in nature, I will revise it for this thread and meet Monique's questionable demand as this is a very important issue.

The cranial size and intelligence link have been substantiated by countless mainstream journals such as Intelligence and the American Journal of Psychiatry. Even Evo should be able to state these are reliable sources. If there is a study in any of the mainstream journals that state the contrary, I am unaware of them. So any thoughts to this? Agree? Disagree?

Some excerpts:

"We now know quite conclusively from MRI studies, for example, that IQ is correlated with brain size, but we still don't know what precisely it is about brain size that causes this correlation."--Kings of Men: Introduction to a Special Issue of the Journal of INTELLIGENCE (1998)
by DOUGLAS K. DETTERMAN (kudos to Mandrake for this one)

"The first of these MRI studies were published in the late 1980s and early 1990s in leading, refereed, mainstream journals like Intelligence (Willerman et al., 1991) and the American Journal of Psychiatry (Andreasen et al., 1993). I know Gould is aware of them because my colleagues and I routinely sent him copies as they appeared and asked him what he thought! For the record, let it be known that Gould did not reply to the missives regarding the published scientific data that destroyed the central thesis of his first edition."--J Ruston

"The published research that most clearly shows the correlation between brain size and intelligence employed MRI, which creates, in vivo, a three-dimensional image of the brain. An overall correlation of 0.44 was found between MRI-measured-brain-size and IQ in 8 separate studies with a total sample size of 381 non-clinical adults. This correlation is about as strong as the relationship between socioeconomic status of origin and IQ. In seven MRI studies of clinical adults (N = 312) the overall correlation was 0.24; in 15 studies using external head measurements with adults (N = 6,437) the overall correlation was 0.15, and in 17 studies using external head measurements with children and adolescents (N = 45,056) the overall correlation was 0.21. The head size and brain size correlation with the g factor itself, which Gould would have you believe is a mere artifact, is even larger --- 0.60! (Jensen, 1994; Wickett et al., 1996).

"Is it reasonable to expect that brain size and cognitive ability are related? Yes! Haug (1987, p.135) found a correlation of 0.479 (N = 81, P<0.001) between number of cortical neurons (based on a partial count of representative areas of the brain) and brain size in humans. His sample included both men and women. The regression relating the two measures is: number of cortical neurons (in billions)= 5.583 + 0.006 (cm3 brain volume). According to this equation, a person with a brain size of 1,400 cm3 has, on average, 600 million fewer cortical neurons than an individual with a brain size of 1,500 cm3. The difference between the low end of the normal distribution (1,000 cm3) and the high end (1,700 cm3) works out to be 4.2 billion neurons. That amounts to 27% more neurons for a 41% increase in brain size. The best estimate is that the human brain contains about 100 billion (1011) neurons classifiable into perhaps as many as 10,000 different types resulting in 100,000 billion synapses (Kandel, 1991). Even storing information at the low average rate of one bit per synapse, which would require two levels of synaptic activity (high or low/on or off), the structure as a whole would generate 1014 bits of information. Contemporary supercomputers, by comparison, typically have a memory of about 109 bits."--J Rushton
 
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  • #2
I still don't understand. Why is this not flawed ? IQ and crane size are related OK nobody doubts. This teach us nothing. Try to correlate crane size with income.
 
  • #3
Correlation coefficients of 0.44, 0.25, 0.15, & 0.479 are terrible and, to me, indicate no correlation at all. Maybe if the correlations were 0.7 or higher, then you would have something to talk about.

Plus, I have yet to hear about a reliable way to quantify IQ.
 
  • #4
Phobos said:
Correlation coefficients of 0.44, 0.25, 0.15, & 0.479 are terrible and, to me, indicate no correlation at all. Maybe if the correlations were 0.7 or higher, then you would have something to talk about.
In terms of g the correlation was found to be .60. But I believe it would be a mistake to dismiss even a .25 correlation so quickly.

And no correlation at all would be 0.00 not 0.25, 0.44, etc.
 
  • #5
Please, could someone explain to me where I am wrong.

You see a correlation between IQ and crane size. I feel this is because those two features are correlated to another more significant one, such as income, or general level of life. That is, somebody with an easier life will both have a larger crane, and a higher IQ. That would clarify everything to me as far as I understand. But everybody seem to ignore my posts, as if I was either totally ununderstandable, or totally non-sens.
 
  • #6
humanino said:
Please, could someone explain to me where I am wrong.

You see a correlation between IQ and crane size. I feel this is because those two features are correlated to another more significant one, such as income, or general level of life. That is, somebody with an easier life will both have a larger crane, and a higher IQ. That would clarify everything to me as far as I understand. But everybody seem to ignore my posts, as if I was either totally ununderstandable, or totally non-sens.

Hi humanino. Be patient. You're probably not being ignored, there's just a lot of posts for people to respond to here at Physics Forums.

I am not convinced that there is a simple & direct correlation between brain size & IQ. They may be somewhat correlated, but life is more complicated then that.

For what its worth, Neandertals had larger brains than H. sapeins but their technology (a possible indicator of IQ) was not as advanced as ours.
 
  • #7
BlackVision said:
In terms of g the correlation was found to be .60. But I believe it would be a mistake to dismiss even a .25 correlation so quickly.

And no correlation at all would be 0.00 not 0.25, 0.44, etc.

Yes, 0 = absolutely no correlation at all, but even random variations can do better than 0.

0.25-0.44 seems to be a very weak correlation and indicates that there are other significant factors involved.

In many other areas of science, I would be inclined to dismiss a correlation of 0.25 (that's getting down into random noise). Getting closer to 0.5 is more interesting, but still indicates that the majority of the contributing factor is missing from the equation.

0.6 is better. Remind me what the g factor is.

A "good" correlation coefficient depends on the type of work. For environmental sampling, reaching 0.7 or higher might be needed for a rating of "good". For some chemical studies, the scientist might demand greater than 0.9. I'm not familiar with what psychiatrists would consider to be good. Perhaps its lower given the complexities of the human mind.
 
  • #8
Thanks for answer Phobos.

I was also afraid that because of my offending post in the previous similar thread (where I commited a personal attack : I was obviously provocating in response to what seemed to me a provocation) people would not read my posts anymore in the biology forum.

I also doubt at all on the significance of IQ tests. I do very well at those (I could easily afford Mensa, but that appear to me as an horrible form of racism, and the people I met there were simply... frustrated), but I think it just measures your ability to conform to normal-thinking. For instance, it does not take into account emotion/sensitivity. A friend of mine which is really clever like to find another logical answer (one not in the list) This is way funnier as well as way more difficult : it requires both logic and imagination.

So IQ does not measure anything anyway.
 
  • #9
The reliabilities (accuracies) of IQ tests

Phobos said:
I have yet to hear about a reliable way to quantify IQ.

  • Degree of agreement can be quantified by the correlation between different observers or between repeated measurements by the same observer. When a correlation coefficient is used this way, it is termed a reliability coefficient, symbolized r[itex]_{xx}[/itex]. The difference between the reliability coefficient and unity (i.e., 1 - r[itex]_{xx}[/itex]) represents the proportion of the total variance of the measurements that is attributed to measurement error.

    It is a common misconception that psychological measurements of human abilities are generally more prone to error or inaccuracy than are physical measurements. In most psychological research, and especially in psychometrics, this kind of measurement error is practically negligible. If need be, and with proper care, the error variance can usually be made vanishingly small. In my laboratory, for example, we have been able to measure such variables as memory span, flicker-fusion frequency (a sensory threshold), and reaction time (RT) with reliability coefficients greater than .99 (that is, less than 1 percent of the variance in RT is due to errors of measurement). The reliability coefficients for multi-item tests of more complex mental processes, such as measured by typical IQ tests, are generally about .90 to .95. This is higher than the reliability of people's height and weight measured in a doctor's office! The reliability coefficients of blood pressure measurements, blood cholesterol level, and diagnosis based on chest X-rays are typically around .50.
(Arthur Jensen. The g Factor. p50.)


Validity and reliability being statistical concepts that are distinct from one another, if you meant valid when you said reliable please specify that.
 
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  • #10
I also see the usual problems with meta-studies...
 
  • #11
What g is, again

Phobos said:
Remind me what the g factor is.
The g factor is the principal statistical component common to multiple cognitive tests of ability. It provides IQ scores with all of their practical validity, such that an IQ score is only worthwhile as a predictor of success in any cognitively demanding domain as far as it is loaded on the g factor.



  • ...g is the sine qua non of test validity. The removal of g (by statistical regression) from any psychometric test or battery, leaving only group factors and specificity, absolutely destroys their practical validity...
(Arthur Jensen. The g Factor. p270.)
 
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  • #12
I swear I have very good results at IQ tests, partly because I have done many. Yet, I have very few doubts that my mental ability is not abnormaly high. I am a PhD student, so I am not totally dumb, but I am sure not a genius. Just contemplate my poor english. I know several persons who have relatively bad results at IQ tests, yet they are really interesting persons : they have quite a cultural-luggage, and also have other skills such as playing and composing music as a miracle. They do not either exhibit an especially slow mind.

I really don't understand this g factor unfortunately. Maybe the tests I had are not good tests. Yet I know they are standard to this Mensa association.
 
  • #13
Let us accept this g factor as an objective measure of intelligence. What about my other objection : I am ready to accept that crane size and intelligence can be related (even though this is not obvious, and Neandertals had larger brains), due to ease of life as explained earlier.

You could find correlations between the size of the vehicle and the size of the house : both are just the result of income.
 
  • #14
humanino said:
I am a PhD student
Just curious :) what do you study?
 
  • #15
this is boring...

It is unfortunately classified in nuclear physics, which leads everybody to think about weapons and nuclear plants.

I am studying the structure of the proton, made up of three quarks. The usual nuclear energy we use today is the residual interaction between protons and neutrons, as the chemical interaction is a residual electromagnetic interaction between neutral systems. The fact that those interactions are residual causes the energy to be weak as well as the process to be dirty (they produce wastes). Electrical energy does not by itself create significant polution for instance. The true interaction is "Chromodynamics" and I am glad to study such a beautifully named theory :rolleyes:

We might hope that, far in the future, we will be able to have a clean and much more efficient source of energy. Of course, for political reasons, as well as probably social choices, we want to consume energy right now, not wait another 50 or 200 years. In turn, that could also be used to build new weapons, but we already have enough to destroy the planet like a hundred times anyway (that is 99 times to much :wink: ), and also biologic weapons appear way more dangerous to me.

There are even people who argue that we could extract an infinite quantity of energy from the vacuum. This is not very well accepted.

Having a new source of energy is required for the exploration of the cosmos, since carrying fuel is a very bad idea. In the very long term, humanity will eventually have to escape its birth planet (if we manage to deal with polution and we don't blow ourselves), because the sun as you know will expand in a red giant and burn our planet.

Did I already wrote all these lines :bugeye: Sorry, I could speak about that forever :shy:

What do you study Monique ? Are you torturing mice :-p
 
  • #16
Thanks for the clarifications, hitssquad.

hitssquad said:
Validity and reliability being statistical concepts that are distinct from one another, if you meant valid when you said reliable please specify that.

Yes, "valid" sounds more like what I meant rather than "reliable". I was thinking in terms of accuracy, not precision.
 
  • #17
humanino said:
It is unfortunately classified in nuclear physics, which leads everybody to think about weapons and nuclear plants.
:bugeye: that all sounds very interesting, ofcourse it would be off-topic to go into that :frown:
I don't torture mice :)
 
  • #18
So what do you study ? Maybe you already said that somewhere else, if you remember you could just post the link. Or maybe your studies are even more secrety than mines :confused:
 
  • #19
It's in my profile :smile: medical biochemistry, involving molecular biology and genetics.
 
  • #20
Phobos said:
Getting closer to 0.5 is more interesting, but still indicates that the majority of the contributing factor is missing from the equation.
Homosexuality is said to have a 0.5 correlation and it seems evident that genetics plays a considerable role in one being homosexual. At least to me it does.
 
  • #21
Average g-loading of standard IQ tests is in the +.80s

hitssquad said:
The g factor is the principal statistical component common to multiple cognitive tests of ability. It provides IQ scores with all of their practical validity, such that an IQ score is only worthwhile as a predictor of success in any cognitively demanding domain as far as it is loaded on the g factor.



  • ...g is the sine qua non of test validity. The removal of g (by statistical regression) from any psychometric test or battery, leaving only group factors and specificity, absolutely destroys their practical validity...
(Arthur Jensen. The g Factor. p270.)
This might be relevant as well:


  • It would seem safe to conclude that the average g loading of IQ as measured by various standard IQ tests is in the +.80s.
(Arthur Jensen. The g Factor. p91.)
 
  • #22
I will do a repost from a lock thread. Folding has been recently link to difference in cognitive performance.

http://www.ncbi.nlm.nih.gov/entrez/...ve&db=pubmed&dopt=Abstract&list_uids=15028646

These results suggest that the leftward pattern of folding is associated with a non-specific performance advantage on cognitively demanding executive function tasks, possibly due to differences in functional interactions between AC/paracingulate cortex and connected frontal regions. It therefore appears that normal variations in brain morphology are associated with individual differences in cognitive abilities.
 
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  • #23
Does anyone know how many of the 'countless' mainstream studies into the relationship between 'cranial size' and _g_ were performed using pre-defined, rigourous double blind protocols?

For the MRI (etc) determination of the 'cranial size', how many studies used automated image processing software to produce unbiased measures of 'size' (presumably volume)?

When (age, gender) sub-groups are analysed, what variation has been found wrt the 'cranial size' / _g_ correlations?

http://www.mugu.com/cgi-bin/Upstream/People/Rushton/rushton-peters.html , which discusses some of the complications involved in nailing down what might naively seem to be a very straight-forward relationship, also seems to suggest that Rushton may have, on occasion, been not such a careful scientist after all (two of BV's four quotes were from Ruston :wink:)
 
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  • #24
crane vs. cranium

humanino said:
Please, could someone explain to me where I am wrong.

You see a correlation between IQ and crane size.

crane
1.
1. Any of various large wading birds of the family Gruidae, having a long neck, long legs, and a long bill.
2. A similar bird, such as a heron.
2. A machine for hoisting and moving heavy objects by means of cables attached to a movable boom.
3. Any of various devices with a swinging arm, as in a fireplace for suspending a pot.
v. craned, cran·ing, cranes
v. tr.
1. To hoist or move with or as if with a crane.
2. To strain and stretch (the neck, for example) in order to see better.
v. intr.
1. To stretch one's neck toward something for a better view.
2. To be irresolute; hesitate.

cra·ni·al
Of or relating to the skull or cranium.

cra·ni·um
1. The skull of a vertebrate.
2. The portion of the skull enclosing the brain; the braincase.

I feel this is because those two features are correlated to another more significant one, such as income, or general level of life.
Ah, the new age of how one feels about science. How do you feel about addition?

I have a suggestion. As a means of learning about a topic, experiment with a few good Internet search engines, or make a habit of visiting your local library. Both resources will enable you to find and read scientific material that pertains to the subject of interest (feeling). The subject of brain volume has been reported extensively in high quality textbooks and scientific journals. You can read about the various MRI and other studies that have been used to measure brain volume and the recent research that has enabled scientist to measure the volumes of specific locations in the brain. After digesting some of that material, you can then meditate and refine your feelings.
 
  • #25
IQ and _g_

hitssquad said:
This might be relevant as well:

  • It would seem safe to conclude that the average g loading of IQ as measured by various standard IQ tests is in the +.80s.
(Arthur Jensen. The g Factor. p91.)

On page 293 of the same book, Jensen wrote: "Because IQ in the general population is correlated around .90 with _g_, the occupational hierarchy obviously reflects _g_ more than any other psychometric factor."
 
  • #26
Thank you Mandrake for the correction about crane and cranial. It was a typo, you may have not noticed that english is not my first language. I hope I misunderstood, because I felt you were making fun of this typo.

I have an original formation in math, and I then turned to physics. So I thought I understand statitistics. It is not the volume of publication that proves the relevance of a aiming-to-be-scientific work. The majority is often wrong.

I don't know what the g factor is, and nobody has explained it to me in a satisfactory fashion so far. I believe, as I explained it earlier, that trying to quantify intelligence is not only impossible, it is dangerous. Let me remind you that Einstein was considered as a bad student, by very respectable teachers in prestigious school.

I am not repeating the same argument again and again. You did not show me why your meta-study is relevant. Russ_waters told he also see the problem. I was worrying to be completely ridicoulus here, so I asked several of my colleague to take a look at those last two threads BlackVision opened. They don't even know I am registered here. It should make you feel less secure that 10 physicists who use statistics everyday at a fairly high level independently had the same objection as I did : you are trying to correlate two variables which obviously result from a more fundamental other variable. Either we did not pay attention enough, or there is something obviously wrong here. I would really like somebody to prove me wrong, but I am afraid this has not occurred so far.

Again, thank you for any correction of my english. I do neither ask correction on every little details which might require many explanations, nor on typos that everybody commits, but I appreciate clarifications on misunderstandings. I am here to learn, and as a scientist my position is sceptic until satisfactory proof.
 
  • #27
Also : what is the purpose of quantifying intelligence ? How would such a quantification have a social use ? Are you not afraid of the use it could have ?
 
  • #28
humanino said:
...I could easily afford Mensa, but that appear to me as an horrible form of racism ...

Why is joining Mensa a "horrible form of racism?"
 
  • #29
humanino:
Thank you Mandrake for the correction about crane and cranial. It was a typo, you may have not noticed that english is not my first language. I hope I misunderstood, because I felt you were making fun of this typo.
I was not making fun of either you nor a typo. I assumed that since you had written the term "crane size" three times that it was not the result of a typing error. You wrote:
I still don't understand. Why is this not flawed ? IQ and crane size are related OK nobody doubts. This teach us nothing. Try to correlate crane size with income.
I am ready to accept that crane size and intelligence can be related (even though this is not obvious, and Neandertals had larger brains), due to ease of life as explained earlier.


To make such an error, you would have to forget to type three letters each time. So, I assumed that you did not understand the definition of "crane."

As for your English, it is outstanding! I admire anyone who can communicate that well in a second language. I have found foreign languages difficult (and not fun) to learn.

Also : what is the purpose of quantifying intelligence ? How would such a quantification have a social use ? Are you not afraid of the use it could have ?

The measurement of intelligence is a useful predictor of academic success, job success, and learning rate. In the US, IQ limits are used to keep people from serving in the military. The lowest intelligence levels allowed are Army 85, Marines and Air Force 88, and the Navy 91. These limits are used because of the difficulty of training when people fall below these points. IQ is useful as a means of sorting through people who are about to enter college to find those who are capable of performing at the levels required by very demanding universities. In the past, US elite colleges selected students largely on the basis of their social class. That is no longer the case after James Bryant Conant (then president of Harvard) set the example of using the SAT to identify students who were capable, but through no fault of their own, were unable to attend high quality secondary schools. Today, very bright students are eagerly accepted to top universities on the basis of their ability, not their social class.

IQ is a useful tool in locating people who should be encouraged to study the most cognitively demanding academic subjects, such as math and physics. Low IQ people have no hope of mastering such fields of study.

The study of intelligence has the potential of allowing society to structure itself in a manner that would be more compatable with the variances that exist in human mental abilities.
 
  • #30
Mandrake said:
To make such an error, you would have to forget to type three letters each time. So, I assumed that you did not understand the definition of "crane."
OK ! Typo means "misattention" I guess. I thought it applied to orthographical errors too.

My concern is that, my own IQ is defined with a [tex]\pm 50[/tex] or more depending on so many factors ! This is from the several tests I have done, because I find it fun. I know a single exam is always unfair, but I think regular school exams as we have in France are more reliable. If you want to study such or such discipline, you have a defined program assigning you to specific competences.

Tigers2B1 : joining Mensa is to me like saying : "I only consider intelligent people worthwhile talking with"

EDIT : OK, maybe I have been exagerating when I said 50. I know the cause of the lower bound in the incertitude but I am not very proud of it :redface:
I should have said 30. But that is still a lot
 
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  • #31
Phobos said:
Correlation coefficients of 0.44, 0.25, 0.15, & 0.479 are terrible and, to me, indicate no correlation at all. Maybe if the correlations were 0.7 or higher, then you would have something to talk about.

Plus, I have yet to hear about a reliable way to quantify IQ.
Health warning! health warning! statistics and damned lies are about to be discussed! Parental discretion is advised!

Here are two time series*:
57643
58206
58737
59266
59827
60353
60878
61435
61958
62479

7298.3
7624.1
8113.8
8586.7
9066.6
9629.4
10021.5
10338.2
10744.6
11472.6

Bill Gates, via XL, tells me that they are highly correlated (r2=0.9954), which is far, far better than 'cranial size' and _g_.

So, I have a very tight correlation - where to from here?

Just as with 'cranial size' and _g_, it seems to me one can only take the next step if one has a theory to test; otherwise, what is the intrinsic meaning of an r2 that is very close to 1?

In the case of 'cranial size' and _g_, we have a physical measurement of a body part of one mammal (this is Biology, not General Physics or Chemistry), and an abstract concept with roots in psychology (to turn up the contrast, NOT neuroscience).

How does the correlation which is the subject of this thread relate to any theories in biology? AFAIKS, it doesn't; it's simply stamp collecting.

{Note to Monique and iansmith: can you please move thread to a more appropriate section of PF? 'Other Sciences', for example.}

*http://sunearth.gsfc.nasa.gov/eclipse/TYPE/pluto.html .
 
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  • #32
humanino said:
...joining Mensa is to me like saying : "I only consider intelligent people worthwhile talking with"

So I take it that you’re joining Mensa.
 
  • #33
humanino said:
Tigers2B1 : joining Mensa is to me like saying : "I only consider intelligent people worthwhile talking with"
Few people socialize with others who have significantly different IQs. In an interview, Jensen put the range of compatability at around 20 points. Some of you may have known Grady Towers (murdered not too long ago). Grady authored a number of interesting pieces, but the best known of them is his THE OUTSIDERS.
http://www.prometheussociety.org/articles/Outsiders.html

I strongly recommend this article to anyone who is highly intelligent. Grady discusses a number of social problems that are associated with very high intelligence. Unfortunately, Grady knew these things from personal experience as well as academic training.

Various papers and textbooks on the subject of intelligence show correlations between spouses and point out that people at one end of the range of IQ distribution are very rarely in contact with those at the other end. I found this to be especially true, since I worked as a physicist. I actually thought that the people around me were just ordinary people. After about 2 decades, I took a job that was not about physics and was shocked at the level of intelligence of the new workers around me.
 
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  • #34
sorry

humanino said:
My concern is that, my own IQ is defined with a [tex]\pm 30[/tex] or more depending on so many factors ! This is from the several tests I have done, because I find it fun.
After reading [thread=35476]this thread[/thread], I realize the fact that I considered IQ tests as a game must explain the variations observed. I did some of those while discussing with buddies in the computer room at school, so maybe I did not pay attention enough. I apologize for spamming this forum with bad arguments :redface:
 
  • #35
Tigers2B1 said:
So I take it that you’re joining Mensa.
why that ? I choose not to after I saw what it is !
 

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