We’ve got a new important paper out in the special issue on race and intelligence in Psych:

Little research has dealt with intragroup ancestry-related differences in intelligence in Black and White Americans. To help fill this gap, we examined the association between intelligence and both color and parent-reported ancestry using the NLSY97. We used a nationally-representative sample, a multidimensional measure of cognitive ability, and a sibling design. We found that African ancestry was negatively correlated with general mental ability scores among Whites (r = −0.038, N = 3603; corrected for attenuation, rc = −0.245). In contrast, the correlation between ability and parent-reported European ancestry was positive among Blacks (r = 0.137, N = 1788; rc = 0.344). Among Blacks, the correlation with darker skin color, an index of African ancestry, was negative (r = −0.112, N = 1455). These results remained with conspicuous controls. Among Blacks, both color and parent-reported European ancestry had independent effects on general cognitive ability (color: β = −0.104; ancestry: β = 0.118; N = 1445). These associations were more pronounced on g-loaded subtests, indicating a Jensen Effect for both color and ancestry (rs = 0.679 to 0.850). When we decomposed the color results for the African ancestry sample between and within families, we found an association between families, between singletons (β = −0.153; N = 814), and between full sibling pairs (β = −0.176; N = 225). However, we found no association between full siblings (β = 0.027; N = 225). Differential regression to the mean results indicated that the factors causing the mean group difference acted across the cognitive spectrum, with high-scoring African Americans no less affected than low-scoring ones. We tested for measurement invariance and found that strict factorial invariance was tenable. We then found that the weak version of Spearman’s hypothesis was tenable while the strong and contra versions were not. The results imply that the observed cognitive differences are primarily due to differences in g and that the Black-White mean difference is attributable to the same factors that cause differences within both groups. Further examination revealed comparable intraclass correlations and absolute differences for Black and White full siblings. This implied that the non-shared environmental variance components were similar in magnitude for both Blacks and Whites.

So, to sum up:

  • Measurement invariance holds per MGCFA, as Wicherts et al demands. It’s also positive with Jensen’s method.
  • We confirm yet again that skin color is correlated with IQ among blacks. This replicates findings going back to early 1900s.
  • Used sibling design to test for causality of skin color and IQ relationship. Causality was not found. This is predicted by hereditarian model, but colorism predicts a within family relationship. Hence, 1-0 in favor of hereditarianism from this test.
  • Sample size was not impressive, it will need replication. Add Health has 1200 normal sibling and 452 dizygotic twin pairs, and the sample is ~25% black, hence there should be ~410 black sibling pairs to use.

Careful readers will know that this is the stuff based on Dalliard’s and Fuerst’s old blogposts (2013!) over at Human Varieties. One of my goals with starting OpenPsych was to get a lot of the science produced by bloggers into journals, so academics would take notice. This undertaking has been moderately successful I think.

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