Educability-and-Group-Differences-1973-by-Arthur-Robert-Jensen

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Technical Misconceptions and Obfuscations 51 extent of the influence of each type of factor depends upon the contribution of the other. Thus the proportional contribution of heredity to the variance of a given trait, rather than being a constant, will vary under different environmental conditions. Similarly, under different hereditary conditions, the relative contribution of environment will differ. Studies designed to estimate the proportional contribution of heredity and environment, however, have rarely included measures of such interaction. (Anastasi, 1958, p. 197) First, a few clarifying comments. The assumption of additivity is not, as Anastasi says, an implicit assumption, it is a very explicit feature of the model for phenotypic variance, viz., P = G + E and o\ = o2+
52 Educability and Group Differences act multiplicatively or for some good reason should be represented as doing so, geneticists would probably stick to the additive model for its greater simplicity, merely by transforming phenotypic measurements to a logarithmic scale. Since adding the logarithms of quantities is the same as multiplying the quantities, P = G x E can be represented in an additive model as log P — log G + log E. If taking the logarithm of IQs (or any other measurements) makes for a better fit of the data to the theoretical expectations called for by the model, then there is no objection to performing this logarithmic transformation (or any other transformation) of the original measurements. For example, two statistically useful criteria commonly sought through transformation are normality of distribution of measurements in the population and the absence of a constant proportionality of the means and variances of population subgroups. Transformation of the scale of measurement to achieve the simplest representation of the data is a standard practice in all branches of science, including genetics.4 The standard model of population genetics, which we have so far presented only in its simplest form, actually includes a provision for estimating non-additive or interaction effects of genetic and environmental factors, as indicated in the formulas: P = G + E + GE (2.10) O ^ + (T^ + G ^ (2.11) P G E GE where GE represents G x E, i.e., the interactive or multiplicative effects of genetic and environmental factors. (Many other nonadditive effects besides multiplicative effects may contribute to the non-additive variance, e.g., yjG x E, log (G + E), etc.) The model attempts to account for as much of the phenotypic variance as possible in terms of additive effects (G + E) and the remainder of the variance that cannot be accounted for (and also cannot be accounted for as arising from epistasis,5 assortative mating,6 covariance of G and E,7 and errors of measurement) is attributed to interaction, i.e., G x E (or GE). The interaction term, GE, reflects either the fact that a unit change in the environment does not produce the same amount of change in the phenotype of every genotype in the population or that a unit change in genetic value does not produce the same change in phenotype at different points on the environmental scale. When attempts are made to estimate
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Educability & Group Differences Art
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THE AUTHOR Since 1957 Dr. Arthur R.
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Ediicability and Group ^
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To the memory of Sir Cyril Burt e d
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List o f Tables 3.1 Correlations am
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Page 39 and 40: Subpopulation differences in educab
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Page 83 and 84: j Intelligence and educability Educ
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102 Educability and Group Differenc
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7 Race differences in intelligence
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8 Multiple and partial correlation
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244 Educabilty and Group Difference
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14 Teacher expectancy Credence in t
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ig Physical environment and mental
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20 Recapitulation The study of abil
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Appendix on Heritability Heritabili
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References a in s w o r t h , m . d
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398 Author Index Davis, A., 300 Dea
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400 Author Index Nichols, R. C., 10
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Author Index 401 Warren, B. L., 120
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cultural deprivation, 258 culture-b
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Making Xs Test of speed and persist
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Stanford-Binet Intelligence Scale,
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