This is a revision of a post from my old blog, substantially updated and expanded.
According to a recent meta-analysis, the correlation between IQ and school grades in the general population is nearly 0.55. Meanwhile the correlation between IQ and years of education in the U.S. is also 0.55. Given the similarity between these two correlations, we can think of them both as just the 0.55 correlation between IQ and academic success.
So in a typical elementary school class (where you have the full range of cognitive ability, including dull students who will drop out later), you might have 30 students, which means that the lowest IQ in the class should be 28 points below average and the brightest in the class should be 28 points above average (IQ 72 and 128 respectively). However because IQ and academic success “only” correlates 0.55, the best and worst students in the class should have IQs only 55% as extreme: 85 and 115 respectively (U.S. norms).
Of course, elementary school grades are only one way we can quantify academic success in the general population. Another way, as mentioned above, is years of schooling or highest degree obtained.
High school dropouts: IQ 85 (U.S. white norms)
In 2006, roughly 17% of American adults, aged 25+ lacked a high school diploma or equivalent. That means that the median high school dropout was in the bottom 8.5% of education. If you’re in the bottom 8.5% of IQ, you’d have an IQ of 80 (U.S. norms), or 20 points below the U.S. mean of 100. But since the correlation between IQ and education is only 0.55, we’d expect high school dropouts to be only 55% as far below the mean, thus have an average IQ of 0.55(-20) + 100 = 89 (U.S. norms)
According to a source provided to me by commenter C, the actual average IQ of Americans with only a 9th to 11th grade education (age 20-90) tested in the WAIS-IV 2006 norming was just as expected: 88.77 (U.S. norms); 85 (U.S. white norms)
University grads: IQ 108 (U.S. white norms)
By 2006, roughly 26% of American adults, aged 25+ had a bachelor’s degree or more. That means that the median university graduate, is in the top 13% of education. If you’re in the top 13% of IQ, you’d have an IQ of 117 (U.S. norms), in other words, 17 points above the U.S. mean of 100. But since the correlation between IQ and education is only 0.55, the expected IQ of university grads would be 0.55(17) + 100 = 109 (U.S. norms).
How close does this prediction come to the actual data? The actual IQ of U.S. university grads (age 20-90) tested in the WAIS-IV 2006 norming was 110.77 (U.S. norms); 108 (U.S. white norms).
PhDs: IQ 119 (U.S. white norms)
In the U.S., a PhD roughly marks the top 1% in years of completed education, which suggests that the median PhD is in the top 0.5% in education level. If there were a perfect correlation between IQ and academic success, we’d expect the average PhD to have an IQ of 138 (the top 0.5%), but since the correlation is “only” 0.55, each point above 100 must be multiplied by 0.55, reducing the expected average IQ of PhDs to about 121(U.S. norms); 119 (U.S. white norms).
The only actual recent data on the IQs of U.S. PhDs that I’m aware of comes from Charles Murray’s book Coming Apart, which reported that for PhDs turning 25-29 in 2005-2009, the average IQ is 124 (U.S. norms). However this is probably too high because (1) Murray’s sample was limited to white PhDs, and (2) the test used was the AFQT, which is arguably an achievement test, not a conventional IQ test, and thus might over-correlate with education. The true average IQ of PhDs is probably several points lower, just as simple regression would predict.
Harvard students: IQ 125 (U.S. white norms)
Are there academic achievements more impressive than getting a PhD? Yes. Getting acceptance into Harvard: the world’s most prestigious university. Out of the 4.1 million 18-year-olds in the U.S. in a given year, only about 1600 go to Harvard. So if there were a perfect correlation between IQ and academic success, the dumbest Harvard student would have an IQ of 150 and the median might have an IQ of 153. However because the correlation is only 0.55, the median Harvard student should be only 55% as far above 100. Thus, simple regression predicts the typical Harvard student should have an IQ of 129 (U.S. norms).
Actually a sample of Harvard students studied by Harvard psychologist Shelley Carson and her colleagues clocked in at IQ 122 (U.S. norms); 120 (U.S. white norms) on an abbreviated version of the Wechsler intelligence scale. On the other hand, Harvard undergrads are rumoured to average 166 on the LSAT, which equates to an IQ of about 132 (U.S. norms). The abbreviated Wechsler estimate is perhaps too low because of ceiling bumping, poor sampling, and an over-emphasis on spatial ability, but the LSAT score may be too high because it’s too much of an achievement test. Averaging them both gives an IQ of 127 (U.S. norms); 125 (U.S. white norms). Very similar to the predicted level.
I completely ignored the stratospheric SAT scores of Harvard undergrads because being selected by this test, it’s an outlier on which they score high by definition.
Tenured professors: IQ 127 (U.S. white norms)
Another form of academic accomplishment that’s about as exclusive as attending Harvard is becoming a tenured university professor. Scientist Steve Hsu wrote:
…when an attorney prepares a case it is for her client. When a Google engineer develops a new algorithm, it is for Google — for money. Fewer than one in a thousand individuals in our society has the privilege, the freedom, to pursue their own ideas and creations. The vast majority of such people are at research universities. A smaller number are at think tanks or national labs, but most are professors…
So in terms of academic success, being a full tenured professor is a one in thousand level accomplishment. If there were a perfect correlation between IQ and academic success, the dumbest tenured professor would have an IQ of 147, and the average tenured professor would probably be around 150. But since the correlation is 0.55, we should expect the average tenured professor to be around 128 (U.S. norms); 127 (U.S. white norms) with quite a bit of variability around that mean, depending partly on the prestige of the university they teach at and the g loading of the subjects they teach.
Academic Nobel Prize winners: IQ 148 (U.S. white norms)
Are there academic accomplishments more impressive than becoming a professor or going to Harvard? Yes: Winning the Nobel Prize. Many years ago a respected psychometric expert named Garth Zietsman wrote an article about using this type of regression to estimate the IQs of Nobel laureates, though I don’t remember the exact stats he used.
But let’s say only one in a million American adults has a Nobel prize (excluding the Nobel peace prize which is non-academic). If there were a perfect correlation between IQ and academic success, we’d expect the dumbest American Nobel laureate to have an IQ of 171 and the average Nobel laureate to be around 174. But again, since the correlation is 0.55, the average Nobel laureate should have an IQ of 141 (U.S. norms); 140 (U.S. white norms).
The only data on the actual IQs of Nobel level scientists is probably outdated. In the Roe study, the average IQ of eminent scientists was 166 on a verbal test (the best proxy for IQ in the study). On the other hand, in the Terman gifted study, the IQ of the two kids who would grow up to win a Nobel Prize was 129 (too low for the study). The Roe study average was probably too high because of the academic nature of the test, and because the sloppy way the test was normed, while the Terman study suffered from too small a sample of Nobel Prize winners perhaps tested at too young an age. Averaging both studies together gives IQ 148 as the best estimate for academic Nobel Prize winners. This is higher than predicted by simple regression from IQ and academic success, perhaps because the data is outdated, or perhaps because at the highest levels, academic achievement becomes more creative, thus increasing the correlation.
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pumpkinperson said:
All those videos could have been combined into a single post, just as a courtesy to the people who are following you from the comment bar.
Afrosapiens said:
me no have self awereness, me drunk
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GondwanaMan said:
Most of that sucks. What’s the point?
Afrosapiens said:
None, I was drunk at a boring party.
Andy said:
Pumpkin Person,
Do you think epigenetics could be an explanation for the Flynn Effect?
RaceRealist said:
Epigenetics, when you really think about it, is Lamarckism. So yea in a way, when a mother is pregnant for instance, diet quality effects the fetus and can lead to negative or positive effects on the fetus depending on diet. That’s a form of epigenetic inheritance.
RaceRealist said:
Here is a nice excerpt from The Blank Slate by Steven Pinker on epigenetics.
“Also inflating the epigenetics bubble is a set of findings that genuinely are surprising, namely that some epigenetic markers attached to the DNA strand as a result of environmental signals (generally stressors such as starvation or maternal neglect) can be passed from mother to offspring. These intergenerational effects on gene expression are sometimes misunderstood as Lamarckian, but they’re not, because they don’t change the DNA sequence, are reversed after one or two generations, are themselves under the control of the genes, and probably represent a Darwinian adaptation by which organisms prepare their offspring for stressful conditions that persist on the order of a generation. (It’s also possible that they are merely a form of temporary damage.) Moreover, most of the transgenerational epigenetic effects have been demonstrated in rodents, who reproduce every few months; the extrapolations to long-lived humans are in most instances conjectural or based on unreliably small samples. Biologists are starting to express their exasperation with the use of epigenetics as “the currently fashionable response to any question to which you do not know the answer,” as the epidemiologist George Davey Smith (2011) has put it. Other deflations of the epigenetics bubble may be found in Coyne, 2015; Heard & Martienssen, 2014; Juengst, Fishman, McGowan, & Settersten, 2014; Moffitt & Beckley, 2015; and Haig, 2007.”
pumpkinperson said:
That’s a form of epigenetic inheritance.
That’s not epigenetics or Lamarckism; that’s just prenatal environment
RaceRealist said:
Right. But it’s, in a way, like it. Lamarckism is when an adaptation gets literally passed from parent to child. I’m stretching the definition a bit, sure, but it still makes sense.
I’m not even a fan of epigenetics, anyway.
pumpkinperson said:
It would be like if lifting weights made you have kids who were naturally more muscular
RaceRealist said:
Three generations after a famine, children were altered epigenetically.
http://www.medicaldaily.com/starvation-and-epigenetics-dna-can-hold-memory-starvation-three-generations-and-now-297054
No studies have been done on this and lifting, but if there is an epigenetic footprint from famines, why not other things? I’m just speculating. Not saying anything definitive.
pumpkinperson said:
Andy, Greg Cochran made a persuasive case against epigenetics as applied to IQ; see 18:18 in below video
Irving said:
this link – http://ocs.fas.harvard.edu/files/ocs/files/law_stats.pdf?m=1429122846 – which no longer works once showed the average lsat for harvard undergrads for the 2012-2013 law school application cycle. it showed that the average *highest* LSAT score was a 168. I say highest because it only counted the highest LSAT score of those who took it multiple times. I can confirm that the number is the same for Yale. At Brown, it has consistently been in the 164 – 166 range – https://www.brown.edu/academics/college/advising/law-school/statistics .
Bruno from Paris said:
Pumpkin,
I’ve just found two independent longitudinal studies on people selected before 13 yo at a 1 in 10 000 level among gifted students. There average IQ is 186. Duke University assessed 2.5 millions pupils who scored above the 3% on achievement tests, selected 425 000 among them and the cohort for the study is only 259. The same as been done with 320 persons selected in the Study of mathematically precocious youth. 12 people belon to both groups. They compare this group of highly gidted HG with a group of people in the top 1% (G) and average population (A).
1) The higher the IQ the higher the average achievement in every aspect of life. Thats very Pumpkin compatible and very controversial among hig IQ people …
Academia :
Chances of getting a PhD/MD/JD : A: 1%. G: 25%. HG : 44%.
Grades obtained in top 10 University : G: 21%. HG : 42%
Examples of achievement : americas top physican list, lawyer having argued more than 10 cases before the supreme court, having produced more than 500 single, national policy advisor of POTUS ….
2) People have a specialized form of intelligence more than a general g (Verbal, Math and Spacial) and it’s better to specialized in one strength. I thought that you emphasize a notion of general intelligence with well rounded individuals . The longitudinal study seems to imply that people with 5 sd in some aspect and 2/2 in the two others (it would be an average of 3) will have a better potential than an average of 4 guy.
3) It seems that SAT is a good tool to select people. It would have been interesting if the same study would exist with Wechsler test and not SAT or GRE. Interestingly, 10% of the people who passed the GRE scored a perfect 2400 wich is 500 times more than the average (knowing they were selected on SAT between 10 and 13 yo).
Click to access Article-PS-Makel-et-al-2016-II.pdf
Click to access Top1in100001.pdf
Bruno from Paris said:
Another interesting study about the validity of IQ prediction is comparaing the group selected before 13 yo on SAT achievement and a group of students selected at graduate level among people with the best grades at the best institutions (with 10 y interval).
– HG +20 have more tenure professors than top graduates + 10.
– They have more people in business earning more than 500 K a year.
So it seems that your hypothesis that there is no negative returns with IQ – wich is extremelly sensisble AND paradoxical among High IQ circles – is true dear PP.
PS : it’s amusing to see that on one article, they use the NBA basket metaphore, that i presented on this site last year.
Click to access PsychScience2006.pdf
pumpkinperson said:
Bruno
It’s a fascinating study and I posted about it in the past.
The only slight concerns I have are 1) they were tested as kids and so they might not be representative of super intelligent adults, and 2) as Mug of Pee pointed out, they may have been helped in life just by being part of the study.
Bruno from Paris said:
Pumpkin,
1) If part of them are not even that intelligent, figures are even more telling (just checked you said that yourself).
2) They’re is a slighlty difference between the two who is supposed to be linked to the Vanderbilt manager intervention
The real problem that i see is maybe SAT math and verbal, even if at that age people are not prepared for it, are biased toward high achiever more than pure intelligent people.
For example, reading the NYT, I found something interesting about Hunter elementary school. They stopped using 100% IQ as the sole factor of selection because their students were not the best performer. Now, they select with testing 5 times the number of slots. And then, they interview people. Here, they can check motivation, interpersonal skills, social environment and lot’s of stuff that matter for success but are not related to intelligence.
Bruno from Paris said:
I understand that the children were pre-selected by the IQ tests and achievements tests given by school to find the top 5% (200 000 people out of 4M each year). And they were tested with SAT without being prepared (because they’re young) . Perhaps in this condition, SAT is more of an IQ test, than 5 years later when people go throug prep school. Another aspect is that SAT allow to select on two distinct intelligent factor Verbal and Math. The big problem is that they miss the spatial intelligence wich is also extremely important ….
Bruno from Paris said:
Another interesting data from those articles is that in math women are
at 1% : 33%, 0.1% : 20% , 0.01% : 6% (16/1).
There is an exception for asian women who are 20% at this level. Author say it is the same data in China. I suspect that it’s because the 0.01% level for white is in fact a 0.1% level among east asian people.
They also found that has this level in math, women were 5 times less likely than men to be involved in hard sciences (math or physics). So the consequence is that they unlikely to reprensent more than 1% of important scientists.
Rahul said:
Pumpkin, how much larger of a practice effect would someone with a 90 IQ have over someone with a 120 IQ?