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

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Race Differences in Intelligence 169 quantized racial dichotomy (Negro = 0 v. white = 1) and SES (if the Negro and white groups are of equal size) is +0-53. (The median SES of the Negroes and whites differs by about one SD.) The usual argument is that SES does not measure the most important environmental variables, which, if included in the SES index, would greatly increase the correlation between the quantized racial variable and the improved SES index. It is most likely, however, that a 12-point SES index pulls along with it many other more subtle environmental factors which are not explicitly measured by the index. Thus many other environmental indices combined along with SES in a multiple regression equation will raise the multiple correlation (R) between ‘environment’ and race (or between ‘environment’ and IQ) only slightly. There are a few environmentally relevant variables on which we can express the (United States) Negro-white difference in terms of standard deviation units, assuming an approximately normal distribution of the variable in both populations. These estimates have been made by Shockley (1969, p. 1432). Based on statistics for all family annual incomes in the U.S. population from $3,000 to $15,000 from 1947 to 1966, the mean family income of Negroes was —0-80±0*15 SDs below that of whites. The SD units by which the Negro mean falls below the white on other variables is: —0-33 for unemployment rate, —0-52 for completing high school, —0-87 for children living with both parents, —1*0 for rate below ‘poverty line’. None of these SD differences comes near the 3-2 SDs (for total environmental effects) or 4-48 SDs (for betweenfamilies environmental effects) derived from the twin studies as being the environmental difference required to produce a 1 SD mean IQ difference between two genetically identical populations. Does a variable seemingly as non-psychological as family income pull along with it enough other factors reflecting the qualities of the environment that would affect children’s mental development such that taking family income into account as an environmental index would improve the prediction of children’s IQs (from the parental IQs) over the prediction that would be derived from a genetic model alone Data which may help to answer this question are found in Terman’s (1926) monumental study of gifted children. In 1922, over 1,500 children with Stanford-Binet IQs of 140 or above were selected from California schools; their educational and occupational
170 Educability and Group Differences careers were followed into adulthood (Terman & Oden, 1959). The Stanford-Binet IQs of more than 1,500 of the children of the gifted group were obtained. These data, therefore, permit an interesting genetic prediction. The simplest additive genetic model used by agricultural geneticists for predicting the mean value of some attribute in the offspring of a specially selected parent population is given by Crow (1970, p. 157), as follows: 0 = M + hl (P-M) (7.1) where 0 = predicted mean of the offspring M —general population mean = narrow heritability9 P = parental mean The population mean, M, is 100. The mean IQ of the gifted group (as children) was 152. Terman estimated their spouses’ mean Stanford-Binet IQ from his Concept Mastery Test as 125. Thus the parental mean, P, would be (152 + 125)/2 = 138-5. The best available estimate of narrow heritability (h2) for intelligence is given by Jinks and Fulker (1970, pp. 342, 346) as 0-71 ±0-01. Substituting these values in the formula given by Crow, we have 0 = 100 + 0-71 (138-5-100) = 127-33 as the predicted mean IQ of the offspring. We can compare this genetic prediction with the mean Stanford-Binet IQ actually obtained by Terman and Oden (1959, Table 61) on 1,525 offspring of the gifted group. The IQ distribution of the offspring is shown in Figure 7.4, with a mean of 132-7 and SD of 16-5.10 The obtained mean is 5-4 IQ points higher than our predicted value. But the prediction was based on the assumption of no difference between the average environment provided by the gifted parents and average environment in the general population. Therefore, the discrepancy of 5-4 IQ points over the predicted IQ may be viewed as due to the environmental advantages of the offspring of the gifted. This would be a ‘between-families’ environmental effect, one SD of which, according to our MZ twin analysis, is equivalent to 3-35 IQ points. So the offspring of the Terman gifted group could be regarded as having enjoyed environmental advantages 5-4/3-35 = 1-6 SDs above the average environment in the
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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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17.3 Theoretical regression lines b
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2 Educability and Group Differences
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10 Educability and Group Difference
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Subpopulation differences in educab
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2 Current technical misconceptions
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j Intelligence and educability Educ
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Table 3.1 Correlations (decimals om
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Table 3.3 Correlations (decimals om
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100 Educability and Group Differenc
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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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