Tag Archives: South Africa

Adjusting South African IQs for malnutrition

25 Tuesday Jan 2022

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By the end of the 20th century, Whites, Indians, Coloureds and Blacks in South Africa averaged IQs of 98, 92, 82, and 69 (UK norms) and malnutrition rates of 5.7, 10.9*, 18, and 32 percent respectively (see table 2.13 below):

From The Global Bell Curve (2008) by Richard Lynn

Malnutrition is defined here as the percentage of the population that is stunted. Stunted is defined as two or more standard deviations (SDs) shorter than comparable healthy populations. In theory only 2% of the healthy reference population should be stunted.

But nutrition is not a discrete variable. In theory there’s a perfect continuum between optimum and suboptimum processing of nutrients and each population has their own bell curve.

So if 32% of South African blacks have sub-optimum nutrition compared to only 2% of well nourished populations, then that tells us that the 32nd percentile (-0.47 SD) on the former’s bell curve equates to the 2nd percentile (- 2 SD) on the latter’s. Assuming roughly equal standard deviations, it suggests South Africa’s black bell curve is shifted 1.53 SD to the left of what was considered optimum at the time.

So the stunted children are just the tip of the iceberg. The average black child in South Africa should be 1.53 SD below his genetic potential in physical growth. What about brain size? Also 1.53 SD below genetic potential? Given the 0.4 correlation between IQ and brain size, this would predict IQ would be 0.4 (1.53 SD) = 0.61 SD below genetic potential. Multiplying by the IQ standard deviation of 15 points, this gives 9 points of impairment caused by malnutrition. Adding this to the IQ 69 of black South Africans gives IQ 78.

I applied the same calculations to all the major groups of South Africa:

It is interesting to compare the estimated black genetic IQ of 78 to the average IQ of 85 for African Americans, a presumably well nourished population judging from the fact that they are virtually indistinguishable from white Americans in height. But genetically African Americans are only 75% sub-Saharan, so adjusting for this, they go from 15 points below IQ 100, to 15/0.75 = 20 points below 100 = IQ 80. In other words, virtually all of the difference between unmixed American and South African blacks vanishes when we adjust for presumably stunted brain size.

Similarly, the IQs of Indians and whites rise to their corresponding levels when reared in the UK (a well nourished country).

*The malnutrition of Indians were estimated from the line of best fit predicting poverty rates in table 2.13 to malnutrition rates in table to 2.13: Malnutrition = 0.65(poverty) – 2.79.

South Africa’s White > Indian > Coloured > Black IQ gap

24 Monday Jan 2022

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[Update Jan 24, 2022: An earlier version of this article incorrectly concluded the students were 13, but with a new chart added to the article, I now conclude they were 14 and adjusted the IQs accordingly]

In their book, The intelligence of Nations, Richard Lynn and David Becker write:

Owen (1992, Table 1) compared intelligence of Coloureds,
Indians, Blacks and Whites from South Africa. The four reported
samples had mean ages of 15.00y and the administered test was the
SPM. Coloureds scored 36.69, which is at the 15.64th GBR-P and
equivalent to an uncor. IQ of 84.86, Indians scored 41.99, which is
at the 30.50th GBR-P and equivalent to an uncor. IQ of 92.35,
Blacks scored 27.65, which is at the 3.96th GBR-P and equivalent
to an uncor. IQ of 73.67, and Whites scored 45.27, which is at the
43.75th GBR-P and equivalent to an uncor. IQ of 97.64. 2.73 had to
be deducted from all four samples for FE-correction, resulted in
cor. IQs of 82.13, 89.62, 70.94 and 94.91.

Here’s the data from the actual study:

Owen, K. (1992). The suitability of Raven’s standard progressive matrices for various groups in South Africa. Personality and Individual Differences, 13(2), 149–159.

For starters, the study never says the students were 15, but maybe they are inferring it from the fact that they are described as Standard 7 pupils.

The same paper was cited by Wicherts et al. (2010) but they listed them as being 16 and mysteriously believe they were tested in 1986 (6 years before publication) giving them a Flynn adjusted IQ of 68.

Wicherts, J. M., Dolan, C. V., Carlson, J. S., & van der Maas, H. L. J. (2010). Raven’s test performance of sub-Saharan Africans: Average performance, psychometric properties, and the Flynn Effect. Learning and Individual Differences, 20(3), 135-151.

Reporting on the same study, Rushton and Jensen believe the students were only 12 to 14, writing:

In South Africa, Owen (1992) found that 1,093 African 12-to 14-year-old high school students solved 28 out of 60 problems on the Standard Progressive Matrices, which is around the 10th percentile, or an IQ equivalent of about 80 (Raven, Raven, & Court, 1998, p. 77).

Rushton should know since he grew up in South Africa, and when I asked two other South Africans, one said 12 to 13, and the other said 13 to 14.

However I found a good source which equates to standard 7 to age 14:

Source

Given the South African Whites, Indians, Coloreds, and Blacks scored about 45, 42, 37 and 28 respectively, these equate to the 45th, 29th, 12th and 2nd percentile of age 14 1979 UK norms (Raven 2000; page 39 to 40), equating to IQs of 98, 92, 82, and 69 respectively.

As we can see from the last row in table 3 below, at age 13.5 to 14.5, the median score in 2008 (50th percentile) is equal to the median percentile in 1979 so no Flynn effect adjustment at this age for post-1979 scores.

Lynn, R. (2009). Fluid intelligence but not vocabulary has increased in Britain, 1979-2008. Intelligence, 37(3), 249–255. 

A cross-cultural study of university students

02 Wednesday Oct 2019

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A 2015 paper by Kate Cockcroft et al., compares the scores of 349 British middle class university undergrads to 107 lower class black South African undergrads on the WAIS-III (UK edition).

The results were as follows:

The UK students averaged a full-scale IQ of 106.95 (UK norms) while the South Africans averaged IQ 93.27. However because this study was published 18 years after the UK WAIS-III was published, we should adjust for the Flynn effect.

The single best source on recent Wechsler Flynn effects is Weiss et al., 2015  which found that full-scale IQ has been increasing by 0.31 points per year, at least in U.S. children. If we assume it’s the same for UK adults, then the UK students have an adjusted IQ of 101 and the South African students have an adjusted IQ of 88.

What’s more interesting to me is how they did on the culture reduced tests since that’s the more fair comparison.

 
Test: Digit Span scaled score Flynn adjusted Digit Span  scaled score Flynn adjusted Digit Span IQ equivalent Block Design scaled score Flynn adjusted Block Design scaled score Flynn adjusted Block Design IQ equivalent Compoite IQ based on adjusted scores on both tests
UK undergrads 9.5 9.32 97 10.66 9.76 99 98
Black South African undergrads 9.35 9.17 96 8.67 7.77 89 91

So on a composite score of the most culture reduced spatial & non-spatial test (Block Design & Digit Span), Black South African undergrads average IQ 91. This is 11 points higher than the average Black South African seems to score on the same culture reduced tests.

As of 2013, only 16% of South Africa’s black young adults were attending higher education (compared to about 55% of whites, 47% of Indians and 14% of Coloureds). Thus, simply attending university puts one in the top 16% of this demographic, with the median South African university student being in the top 8%. If there were a perfect correlation between IQ and education, the median South African black university student would have an IQ 21 points higher than the average black South African. In reality his IQ is only 11 points higher, suggesting a correlation of 0.52 (at least on the most culture reduced tests).

This is similar to the 0.57 correlation between IQ and education observed in the United States.