Here’s a new and fascinating (if intellectually challenging for me lately—I’m more into Fireworks Explosions these days) preprint scientific paper on racial admixture and cognitive performance, in the vein of the earlier admixture analysis of the Philadelphia Neurodevelopmental Cohort that I posted about in 2019. This new admixture study is of 9,972 children in the national Adolescent Brain Cognitive Development study (ABCD).

Linear and partially linear models of behavioural trait variation using admixture regression

Version 2, June 17, 2021

Gregory Connor, Maynooth University

Bryan J. Pesta, Cleveland State University

Abstract

Admixture regression methodology exploits the natural experiment of random mating between individuals with different ancestral backgrounds to infer the environmental and genetic components to trait variation across culturally-defined racial and ethnic groups. This paper provides a new statistical framework for admixture regression based on the linear polygenic index model widely used in behavioural genetics. Using this framework we develop a new test of the differential impact of multi-racial identities on trait variation, an orthogonalization procedure for added explanatory variables, and a partially linear semiparametric functional form. The methodology is illustrated with data from the Adolescent Brain Cognitive Development Study. …

The Adolescent Brain Cognitive Development Study (ABCD) is a collaborative longitudinal project between 21 sites across the US. Its goal is to further research into the psychological and neurobiological basis of development. At baseline, around 11,000 9-10 year old children were sampled, using a probabilistic sampling strategy, from public and private elementary schools and through non-school-based community outreach between 2016 and 2018, with the goal of creating a broadly representative sample of US children of this age. Children who were not fluent in English (or whose parents were not fluent in either English or Spanish) were excluded, along with those with severe medical, neurological, or psychiatric conditions.

They have both DNA ancestry and Self-Identified Race/Ethnicity for the sample. In this table, the child’s race/ethnicity according to the parent’s identification is listed in the leftmost column and the racial ancestry from the DNA are across columns.

For example, the 5,498 subjects who self-identified as only non-Hispanic white averaged 9.93 years old, had genes suggesting 97% European ancestry, 1% African ancestry, 1% South Asian ancestry, with “neuropsychiatric performance” of 0.25 standard deviations above average, and a socio-economic-status 0.41 standard deviations above average.

The NIH Toolbox (NIHTBX) neuropsychological battery was designed to measure a broad range of cognitive abilities. It consists of seven tasks which index attention (Flanker Inhibitory Control and Attention Task), episodic memory (Picture Sequence Memory Task), language abilities (Picture Vocabulary Task & Oral Reading Recognition Task), executive function (Dimensional Change Card Sort Task & Flanker Inhibitory Control and Attention Task), processing speed (Pattern Comparison Processing Speed Task), and working memory (List Sorting Working Memory Task) (Akshoomoff et al., 2014; Weintraub et al., 2013). NIHTBX was normed for samples between ages 3 and 85; tasks correlate highly with comparable ability assessments (Weintraub et al., 2013). Moreover, this battery has been shown to be measurement invariant across American ethnic groups (Lasker, Pesta, Fuerst, & Kirkegaard, 2019).

Here are a couple of interesting graphs. This first one shows African ancestry percentage from DNA along the horizontal axis:

This shows that American children have three peaks for African ancestry. Reading from right to left, a number are around 83% black (presumably, regular African-Americans with no white parents or grandparents), around 42% black (presumably, one regular African-American parent and one non-black parent), and quite a few with a few percent black ancestry. (People with a little black ancestry, presumably who don’t identify as black—i.e., an ancestor passed; I’ll try to go back to figure out if this includes Hispanics later.)

Here’s a graph of the average neuropsychological battery score on the vertical axis and the percent African ancestry on the horizontal axis.

This shows a negative correlation between admixture of African ancestry, except at the near 100% black level. I’m guessing that 100% black children tend to be of recent black immigrant stock.

It would be interesting to see a scatter plot of this data. The 2019 study’s scatter plot showed a lot of variation.

I will keep grappling with this paper, which is pitched around my cognitive ceiling.