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View Diary: Heritage study co-author wrote paper on 'substantially lower' IQ of Hispanic, other immigrants (194 comments)

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  •  uh, what? (1+ / 0-)
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    stevemb

    You seem to be the only person here so far to use the word "heritability," so I can't tell what your point is.

    That said, the Wikipedia article to which you linked says in the third sentence,

    There has been significant controversy in the academic community about the heritability of IQ ever since research began in the 19th century.
    So I really can't tell what your point is.

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    by HudsonValleyMark on Wed May 08, 2013 at 12:15:30 PM PDT

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    •  It was controversial. (0+ / 0-)

      Not so much anymore, given our vastly better understanding of genetics.  As the rest of the article mentions, 0.85 for adults is pretty commonly agreed upon and confirmed by twin studies.

      I mention "heritability" because that's what's you can gather empirical evidence for, as you're never guaranteed a complete isolation of genetic factors (certainly not in the real world.)

      •  Be careful with what you mean by (1+ / 0-)
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        HudsonValleyMark

        "heritability". It is a highly technical term referring to the proportion of variability in the scores of a particular population that can be explained by genetics. Thus if (to make up some figures) we say that the heritability of IQ in white Americans is .85) that means that if you took one group randomly selected from white Americans, and another group of white Americans who were genetically identical, and administered IQ tests to everybody in both groups, the variance of the second group's scores would be only 15% of the variance of the first group's scores.

        This is not controversial; there is in fact a very strong relationship between someone's IQ score and his/her immediate ancestors' IQ scores. The problems come when people try to make invalid extrapolations from this fact.

        The first such fallacy is to assume that between-group differences in average IQ scores must have the same causes as within-group differences in individual IQ scores (and heritability only applies to the latter). But those are two completely different types of variation, and group averages do not, except by coincidence, stastically behave the same way as individual measurements. Thus heritability cannot, by itself, explain between-group differences.

        The next fallacy is to claim (as Murray and Herrnstein did) that heritability says anything about how much group average scores (or even individual scores) could be affected by changes in environment. It simply does not. Heritability values are only valid within the particular range of environments that the population in question currently experiences. They can be, and often are, different in different environments. If you think of 1 - heritability as the environmental contribution to IQ variability, it's the contribution of variation in the population's current environment, not of variation in all possible environments that the population might be subject to.

        Finally, and again Murray and Herrnstein were guilty of this, heritability cannot be used to partition an individual score or even a group mean into genetic and environmental components. It's a measure of variation and as such can only be applied to a collection of observations. It's essentially a squared standard deviation. If I step on the scale and it reads 205 pounds, it's totally meaningless to talk about the standard deviation of that reading.

        Once again, heritability is a measure of how much less "spread out" the observations on a group of genetically similar people experiencing a particular environment will be compared to a group of genetically dissimilar people experiencing that exact same environment. It does not describe the limits of the differences that could result from changing that environment, nor does it describe anything about any individual observation.

        Sometimes truth is spoken from privilege and falsehood is spoken to power. Good intentions aren't enough.

        by ebohlman on Wed May 08, 2013 at 07:53:41 PM PDT

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      •  just to say (0+ / 0-)

        First of all, to say that "the rest of the article mentions" that "0.85 for adults is pretty commonly agreed upon" is a stretch. The article twice attributes that figure to a particular 2004 meta-analysis. Moreover, as you know, much of the controversy isn't about choosing a point estimate (or even a range).

        Second, to say that heritability is what we can gather empirical evidence for doesn't establish any obvious connection to the diary.

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        by HudsonValleyMark on Thu May 09, 2013 at 07:42:08 AM PDT

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