A reader sent me the following email:
Hello PumpkinPerson,
I have been reading your blog off-and-on for the last 5-6 years and I’ve seen that you’ve started to estimate reader IQs from their histories and test scores and I was curious what you would estimate mine to be. I’ve written a history that I think contains the majority of the most pertinent information for your approximation. I’m sorry if I wrote too much but I wanted to give as much information as possible.
Biography: I am black male in my early 30s who is currently in his 4th year of a PhD program in psychology (my program is not elite at all and is roughly #100 in the US grad school ranking for my field) after getting my BA in the same from a top 60 college. I grew up upper-middle class and have lived in multiple countries but am mono-lingual and have spent most of my life in the US. I could read the bible at the age of 5 and I was able to read at a college level by the time I was in middle school. My math ability has lagged behind notably, however. I was better than most of my peers at math but I was not truly exceptional by any means. My family is religious but I have been an atheist since I was 14.
About 520,000 black Americans become old enough to get a PhD every year, but of these, only 2,512, did so in 2019. This puts the median black PhD in the top 1,256, or one in 414 level (+2.8 SD level). Assuming a 0.68 correlation between IQ and years of education, we’d expect your IQ to be 0.68(+2.8 SD) = +1.9 SD above the black mean.
Given that U.S. blacks have a mean WAIS-IV IQ of 87.7 with an SD 14.4 (U.S. norms), +1.9 SD = IQ 115.
According to page 374 of Charles Murray’s Coming Apart, blacks with PhDs or professional degrees average IQ 112.2 (U.S. norms)
You also write:
Physical characteristics and health: I am 5’10 and my head circumference is around 60.5cm. I think this should be taken with a grain of salt though since my head is very long and fairly narrow which should deflate actual brain volume. I was very overweight until I was around 20 years old at which point, I lost a lot of weight and have vacillated between 160-185 since and am roughly 180lbs right now. I have a history of depression and anxiety and have diagnosed epilepsy.
605 mm circumference implies a 192.5 mm cranial diameter, however because your circumference was measured in-vivo, I subtract 11 mm for fat and skin around the skull. This reduces it to 181.5 mm which implies a true circumference of 570.2 mm. Below is the curve predicting brain size from head circumference:
Source: Figue 3 in Jørgensen, J. B., & Quaade, F. (1956). External cranial volume as an estimate of cranial capacity. American Journal of Physical Anthropology, 14(4), 661–664.
The above curve predicts you’d have a cranial capacity of about 1676 cc according to an equation I created from said curve:
cranial capacity = 0.0080(head circumference)^2 – 1.9(head circumference) + 158
However because of ethnic and gender differences in head shape, I would multiply this figure by 0.915, reducing it to 1534 cc. This is still over 227 cc above the mean for young black men circa 1980 and probably about 174 cc above young black men today, putting you in the 97 percentile (+1.91 SD). Such a large brain may help explain your epilepsy because of the enhanced electrical activity.
Assuming a 0.4 correlation between IQ and within-sex brain size, this predicts an IQ of 0.4(+1.9) = +0.76 SD above the black mean, or IQ 99.
Conclusion:
Estimated IQ of black American PhD: 115
Estimated IQ of black American with very large (1534 cc) brain size: 99
Estimated IQ of black American with both: 119
So 119 would be what I’d expect based on your two most salient biodemographic IQ correlates, but in part 2 we’ll discuss your actual test scores and see how close this prediction comes.
Pumpkin Person 
My PS is only low because of my depression. When I feel completely energized my catatonic state goes away. I’m like 120 then.
“About 520,000 black Americans become old enough to get a PhD every year”
Pepe what kind of logic is this? A Ph.D. isn’t like high school where basically everyone other than Rick Rosner finishes at a specific age. You have some people who complete it in their early 20s and others who come back to school to get it in middle age or later.
There’s not even a single threshold age, really
Those who get one early and those who get one late cancel each other out
Not that it really matters statistically, but what are you using as the center of mass here? 30?
I don’t have any given age in mind. As long as the age cohorts for the past few decades have been roughly equal in size and the number of PhDs allotted per year has been roughly constant, this should tell me roughly what percentage of black Americans from recent generations, gets PhDs.
And even if it didn’t cancel out and the PhD cohort average age would go up or down, it wouldn’t change anything by itself to your math.
Only a variation in the absolute number of PhD or the size of the black cohort or the the proportion of foreigners have an impact mutatis mutandis on this math.
Does it happen to me to ask illogical questions Pumpkin (I know I ask very naive questions sometimes) ?
No you’re super logical, but you sometimes say things which are very strange, which causes pill to assume you lack social IQ.
It is relevant if the black birthrate was changing around 30 years ago
That’s why PP wrote every year (whether it’s true or not, i don’t know if the number has staid the same).
The selection rate for today’s PhD is more accurate taking the number of people borned 30 years ago.
But for « threshold age » impact on selection base size, only the variation in the cohort of black each year matters whether they come from black women birthdate (mainly) or black anchor babies or black « dreamers » (if they are not accounted as foreigners) or whatever cause the number of potential non foreigner black people to vary.
Another question is that for the result in itself, I guess it’s the second step, correlation in years of education and IQ, that can be the main source of variation.
My guess would be that this figure is going down in general for university level of education and even more so for PhD level.
Those careers are less attractive since gifted employees have better and better opportunities elsewhere and few high paying jobs look specifically for PhDs (unlike D.E.Shaw). Until the 70ies, only entrepreneurs and people with capital could get a huge income, even in law or finance. Not anymore.
I guess for the same reason university professor, despite tenure, and Nobel prize holders, despite prestige, IQs is also going down .