Conceptual starter kit for thinking about genes, race, and IQ test scores III

The most common argument made by researchers for thinking that differences among IQ scores between races might be genetic is flawed (see previous post), but, in case you find yourself slipping back to thinking it’s plausible that the differences between races in average scores is genetic, take note of the following lesson from a statistics textbook by Lindman:

Consider a case of high school students’ test scores in algebra viewed in relation to their teacher and school.  The students within a school are randomly assigned to a teacher in their usual school.  Lindman notes that a significant difference among school averages “is likely to be interpreted as due to differences in physical facilities, administration, and other factors that are independent of the teaching abilities of the teachers themselves…  [However, d]ifferences between teachers in different schools are part of the [average school difference], and the observed differences between schools could be due entirely to the fact that some schools have better teachers [or] some schools have smarter children attending them” (Lindman 1992, 194).

(Lindman could have added that the observed differences between schools could be due entirely to combinations of factors, such as students responding worse to teachers whose attention is distracted because their school’s administrators insist more on detailed documentation of student performance, and so on.)

In any case, analysis of data cannot help researchers hypothesize about factors causing the difference in the average scores from one school to the next when the teachers are replicated (in their students’ test scores) only within schools.

To translate this into the concerns of this talk, researchers cannot hypothesize about factors causing the difference in the average scores from one race to the next when all individuals in one race are never raised as individuals of another race—we can’t take a pair of identical twins and randomly assign them to be treated, say, as Asian-American and African American.

Reference

Lindman, H.R.: 1992, Analysis of Variance in Experimental Design, Springer-Verlag, New York.

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One thought on “Conceptual starter kit for thinking about genes, race, and IQ test scores III

  1. Chuck

    Ok,

    I read over a few of your papers. You make some good points. I don’t have access to (1), so I will comment/inquire based on what I can glean from (2).

    First, I will reiterate the point I made before, When it comes to the B-W gap, Flynn presupposes (minor) average genetic differences whether in disposition or capacity and the soundness of his model of heredity . As he sees it, these minor differences snowball over time. Whether his model of heredity in this particular instance is more plausible, at this point in time, than the often assumed one is a complex question. To the extent it’s not, Jensen’s argument stands (since we are dealing with plausibility).

    When it comes to your discussion of heredity you note:
    1. High heritability of a trait does not imply that it is hard to change through environmental changes.

    This is an important point. But as my concern is ultimately moral and ethnic, it’s not particularly relevant; I’m interested in the cause of the present gap and, if you will, culpability — which is surely oft assumed these days — not the ready potentiality of altering it. (From your perspective that might be silly, but I take the issue, and charge of iniquity, seriously — but perhaps taking it seriously is the mistake as the whole popular discourse seems to be riddled with some type of mauvaise foi when it comes to individual versus group rights and mala fides when it comes to assigning culpability).

    Moreover, I don’t see how the fact that highly heritable traits are malleability effects Jensen’s arguments. The environmental factors that could differentially raise the intelligence of one population relative to another living in the same environment would be X-factors (or in Flynn’s model gene-environment X factors)

    2. As plots of possible ‘norms of reaction’ make clear, the differences among varieties and their relative ranking can change from a subset of the locations to the full set.

    Perhaps I misunderstand the Norms of reaction model; my impression is that this model presupposes average genetic differences.

    3. As a reiteration of the observed trait/measurable factor distinction (theme #3), let us note that, although effects associated with varieties are often called ‘genetic’ effects, this label is potentially misleading because the differences between variety effects cannot be translated in any direct fashion into hypotheses about specific genetic factors.

    I don’t understand this. I think you are saying that you can’t deduce a specific causal pathways for a found trait differences. (A “heritable” difference in general intelligence could be due to, say, a genetic difference in temperament — in the sense of active heredity).

    4. Admittedly, in some situations heritability can be calculated as a ratio of ‘genetic’ variance to total variance for the trait (phenotypic variance), but genetic variance in this context refers to the variance of variety effects (using the agricultural terminology of this commentary) not to the variance of specific measurable genetic factors

    This seems to be the same point as in 3. If this is the point, I would note that there are multiple lines of evidence that indicate that g is under direct genotypic control. (For example: Sowell, et al.,1999. In vivo evidence for post adolescence brain maturation in frontal and striatal regions.) While this doesn’t show that differences in g are due to differences in genotype, it lends to the plausibility of the idea.

    Regardless, 3 /4 is a good point and worth emphasizing, but I don’t see how this (and the larger point with Jensen) implies your statement (above) that:

    “To translate this into the concerns of this talk, researchers cannot hypothesize [obviously you can hypothesize — you just can’t conclude] about factors causing the difference in the average scores from one race to the next when all individuals in one race are never raised as individuals of another race—”

    On the face of it, this statement implies that you can’t conclude anything about the environmental vrs. genetic etiology of differences between individuals — since no two individuals are raised the same. But surely ANOVA lets you conclude something (within group), just, as you note, not pecific genetic causal pathways. Given this, when we are talking about between group comparisons, we return to Jensen’s argument (or a variant of it) — as I understand it. That fact that there is (apparently) no X-factor that can account for group difference, and the fact that there is a high heritability within groups mean that there must be some average genetic differences — and this is what you can conclude.

    But maybe I’m thinking about this incorrectly.

    Reply

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