Our next step was to examine separately the results from the three test years (1986, 1988, and 1990). For the children who were 6 or older when they took the test (which again shows a smaller difference than when the test includes all children), the B/W differences for the three test years, using sample weights, were 5.9, 1.9, and 3.0 points, respectively. The differences across test year did not affect the conclusion that a significant dysgenic effect exists, but the reasons for the differences are worth investigating.
In our attempt to see whether the dysgenic effect could be attenuated, we repeated all of these analyses with one difference: Instead of using the national norms for the PPVT (normed to a mean of 100 and SD of 15), we let the NLSY children be their own reference group, comparing the black and white scores using the observed mean and standard deviation for all NLSY children who took the test. This procedure reduces the estimate of the dysgenic effect. For example, the results, using sample weights, for the children who were 6 and older, showed an increasing B/W gap of 1.9 points instead of the 3.9 points produced by using the national norms. The difficulty in interpreting this finding is that the procedure itself has no good rationale. The PPVT national norms seem to have been properly determined. If anything, the Flynn effect should mean that the NLSY children, taking the test anywhere from seven to eleven years after the norms were established, should have a 2- to 3-point IQ edge when compared to the national norms. So we have no reason to think that the lower estimate is the correct one, but it does represent the best way we could concoct to minimize the B/W dysgenic effect.
Finally, we explored how the births to NLSY women might affect these findings by comparing black and white women who had not borne a child as of 1990. The mean IQ for the childless white women was 106.6, compared to 100.3 for childless black women. That black women without children have a mean of 100 is in itself striking evidence of the low fertility among the top part of the black IQ distribution, but even if subsequent fertility for the two groups is the same, the B/W gap in the next generation will presumably continue to diverge as the NLSY women complete their fertility.
47 New York Times. “Slighting words, fighting words.” Feb. 13, 1990, p. A24.
48 The computation in the text counts each mother as many times as she had children who were tested. If instead each mother is counted only once, the white-black difference among mothers is 1.12 SDs. The white-Latino difference is 1.05 SDs.
49 Auster 1990; Bouvier 1991; Gould 1981; Simon 1989; Wattenberg 1987; Wattenberg and Zinsmeister 1990.
50 Holden 1988.
51 E.g., Higham 1973; Lukacs 1986.
52 Simon 1989. For a symposium, see Simon et al. 1993.
53 Auster 1990, and various contributors in Simon et al. 1993.
54 Bouvier and Davis 1982. This particular estimate is based on annual immigration of 1 million.
55 The figures for the 1950s, 1960s, and 1970s were 11 percent, 16 percent and 18 percent respectively. SAUS 1992, Table 14 (SAUS 1971, Table 4).
56 Lynn 1991.
57 SAUS 1992, Table 8. The figures also includes once-illegal immigrants who were granted permanent residence under the Immigration Reform and Control Act of 1986.
58 Sowell 1981.
59 A first, elementary consideration is that the NLSY data refer almost exclusively to the children of the adults who decided to immigrate. Whatever self-selection for IQ might have existed in the elders will be less visible in their offspring.
60 Carliner 1980; Chiswick 1978; Gabriel 1991.
61 Borjas 1987. Borjas’s formulation also draws on Roy 1951 and Sjaastad 1962. In forthcoming papers, Borjas has since extended his analysis through the 1990 census, showing a continuation of the trends from 1970 to 1980. Borjas 1993, 1994.
62 Borjas 1987, Table 3.
63 Sowell 1981, p. 220.
64 Borjas 1987, Table 3.
65 Borjas 1987, p. 552.
66 The procedure is limited to the NLSY’s cross-sectional sample (i.e., omitting the supplemental samples), so that sample weights are no longer an issue. Using random numbers, subjects with IQ scores above 97 had an equal chance of being discarded. Because different subsamples could yield different results, we created two separate samples with a mean of 97 and replicated all of the analyses. The data reported in the table on page 368 represent the average produced by the two replications, compared to the national mean as represented by unweighted calculations using the entire cross-sectional sample.
67 Cattell 1938, as reprinted in Cattell 1983.
68 Cattell 1983, pp. 167, 168.
69 Cattell 1983, pp. 167, 175.
70 Cattell 1983, pp. 167, 169.
71 The procedures parallel those used for the preceding analysis of a mean of 97.
72 In effect, our sample with a mean of 97 shows what happens when people with above-average IQs decrease their fertility, and our sample of 103 shows what happens when people with below-average IQs decrease theirs. When we changed the NLSY sample so that the mean fell to 97, we used a random variable to delete people with IQs above 97 until the average reached 97. This did not do much to get rid of people who had the problems; most of its effect was to diminish the supply of people without problems. When we changed the NLSY sample so that the mean rose to 103, we were randomly deleting people with IQs below 103. In the course of that random deletion, a significant number of people toward the bottom of the distribution—our Classes IV and V—were deleted. Suppose instead we had lowered the IQ to 97 by randomly duplicating subjects with IQs below 97. In that case, we would have been simulating what happens when people with below-average IQs increase their fertility, and the results would have been more closely symmetrical with the effects shown for the 103 sample.
73 These figures continue to be based on the cross-sectional NLSY sample, used throughout this exercise. The 1989 poverty rate for the entire NLSY sample, calculated using sample weights, was 10.9 percent.
Chapter 16
1 A woman was classified as a chronic welfare recipient if she had received welfare for at least five years by the 1990 interview. Women with incomplete data on AFDC in the years following the birth of the first child or whose first child was born after 1985 were not scored on this variable.
2 We do not weight the computations for the overrepresentation of below-average IQ mothers, but we continue to use sample weights.
3 This represents the mean of the mothers of the NLSY children, with each mother counted once for each illegitimate child. Because of the inverse relationship between IQ and the number of illegitimate children, the mean counting each mother of an illegitimate child only once was higher: 89.
4 As in the case of illegitimacy, IQ and the number of children of divorced and separated mothers were inversely related. When the mother is counted only once regardless of the number of children, the mean is 94.
5 See Chapter 10 for a description of this intelligence test: (the PPVT).
Chapter 17
1 A brief refresher (see Chapter 4) : A heritability of 60 percent (a mid-range estimate) says that 40 percent of the observed variation in intelligence would disappear if a magic wand wiped out the differences in those aspects of the environment that bear on intelligence. Given that variance is the standard deviation squared and that the standard deviation of IQ is 15, this means that 40 percent of 152 is due to environmental variation, which is to say that the variance would drop from 225 to 135 and the standard deviation would contract to 11.6 instead of 15 if all the environmental sources of variation disappeared.
2 “A healthy mind in a healthy body.” Some of the history is recounted in Lynn 1990b. Abstracts of a series of studies by Stephen Schoenthaler and his associates on the effects of diet on intelligence and on antisocial, criminal behavior are in Schoenthaler 1991.
3 Stein et al. 1972.
4 Lynn 1990b.
5 Benton and Roberts 1988.
6 At the age of 12 and 13, youngsters’ scores rise during an eight-month period in the natural course of even
ts. The dietary supplement, then, is affecting the rate of increase of the nonverbal, but not the verbal, scores.
7 Schoenthaler et al. 1991.
8 WISC-R. Block Design, a highly g-loaded subtest of WISC-R, showed little or no benefit of the food supplement.
9 Earlier work suggesting that reductions in refined sugar increase intelligence are now being reinterpreted as the effect not of sugar per se but of shifting the diet away from foods with little in the way of vitamins and minerals to more nutritious foods; see Schoenthaler et al. 1991; Schoenthaler Doraz, and Wakefield 1986. The basic point is that we have almost no idea of the pathway between diet or food supplements and intellectual development; assuming there is a path, it could be long and winding.
10 A child taking a pill that gives, say, one RDA is getting more than the recommended daily allowances, since the rest of his diet cannot be utterly devoid of vitamins and minerals.
11 For a failure to confirm an effect of vitamin-mineral supplements, see Crombie et al. 1990, and for a failure to find an effect on intelligence of diet short of chronic malnutrition, see Church and Katigbak 1991. For more general discussion of the issue, see Eysenck 1991; Lynn 1990; Yudkin 1991.
12 Later children are on the average born into larger families, which tend to be of lower average IQ. Hence, there is a decline with successive births that is a by-product of family size in and of itself. However, even after the family size effect is extracted, there may be a decline with birth order. The classic demonstration of declining scores with successive births independent of family size is a study based on a large sample of Dutch men (Belmont and Marolla 1973; Belmont, Stein, and Zybert 1978). Since then, subsequent studies have both confirmed and failed to confirm the basic relationship (e.g., Blake 1989; Retherford and Sewell 1991; Zajonc 1976). At present, there is no resolution of the varying findings.
13 Representative findings, on Japanese twins, are in Takuma 1966, described in Iwawaki and Vernon 1988.
14 For a review of the literature on twin differences in birth weight in relation to IQ as well as of other evidence that the uterine environment affects intelligence, see Storfer 1990.
15 Achenbach et al. 1990. This study compared two dozen low-birth-weight babies whose mothers received training in mothering with comparably small groups of normal-weight babies and low-birth-weight babies whose mothers did not receive the training. The encouraging outcome is that when the children were 7 years old, the usual deficit seems to have been forestalled by having trained the mothers in infant nurturing. However, the small scale of the study, the lack of random assignment to the three groups, and the puzzling near identity in scores for the underweight children whose mothers had been trained and the normal children suggest that the next step should to attempt to replicate the finding, as the authors themselves say.
16 For a helpful and balanced introduction to aptitude-treatment interactions, see Snow 1982.
17 Hativa 1988.
18 Atkinson 1974.
19 Cook et al. 1975.
20 Coleman et al. 1966. The report talked about educational “aptitude,” but the measures used—vocabulary scores, reading comprehension, mathematical reasoning tasks, etc.—were taken from standard group tests of IQ.
21 See Mosteller and Moynihan 1972 for a collection of more or less critical articles; included also is Coleman’s response to the most intense methodological criticisms (Coleman 1972). The combatants were often trying to answer different questions, with Coleman mostly interested in whether the objective differences among schools were responsible for the observed differences in abilities and his critics more interested in characterizing the objective differences in the schools. We cannot do justice to the range of issues that surfaced in the report and the subsequent commentary, but one of them deserves mention: The report uncovered evidence that the ethnic and socioeconomic mix of students in a school had a larger impact than the more standard investments in per pupil expenditures, teacher salaries, quality of physical plant, and the like. This, in turn, became a major argument for school busing. Soon after, school busing itself became a battleground for social researchers, a tale we will not tell here except to say that having a beneficial effect on intelligence is no longer used as an argument in favor of busing.
22 Coleman and Hoffer 1987.
23 It isn’t hard to find what seems to be the opposite conclusion in educational writings (e.g., the Coleman report is “no longer taken seriously,” Zigler and Muenchow 1992, p. 62) but no one has been able to show that the variables examined in the report account for much of the variation in cognitive ability among American public school students. If they are in any sense not taken seriously, it is presumably because educational variables other than the ones that Coleman studied have been found to be significant. This chapter reviews the evidence about those other variables as well.
24 See Kozol 1992 for a passionate argument that disparities in school funding are a major cause of disparities in educational outcomes.
25 Husén and Tuijnman 1991.
26 The quantitative details of the study are not germane to contemporary times, but even then, when schooling varied so broadly, the direct link between IQ at the age of 10 and at 20 was a minimum of five times stronger than that between amount of schooling and IQ at 20, in terms of variance accounted for in a path analysis.
27 Flynn himself does not believe that educational equalization per se accounts for much of the rise in IQ in some countries such as Holland (Flynn 1987a), but then Flynn also does not believe that the rising national averages in IQ really reflect rising intelligence.
28 Stephen Ceci (1991) has summarized evidence, much of it from earlier in the century, for an impact of schooling on intelligence.
29 National Center for Education Statistics 1981, Table 161, 1992, Table 347.
30 McLaughlin 1977, p. 55.
31 McLaughlin 1977, p. 53 The failure of such compensatory efforts antedated the Great Society by many years, however. An early educational researcher writing of similar compensatory efforts in 1938 concluded that “whatever the number of years over which growth was studied; whatever the number of cases in the several groups used for comparisons; whatever the grade groups in which the IQs were obtained; whatever the length of the interval between initial and final testing; in short, whatever the comparison, no significant change in IQs has been found” (Lamson 1938, p. 70).
32 Office of Policy and Planning 1993.
33 For more on this distinction, see Adams 1989; Brown and Campione 1982; Jensen 1993a; Nickerson, Perkins, and Smith 1985.
34 “Chicago educator pushes common sense,” St. Louis Post Dispatch, Dec. 2, 1990, p. 5D; “Marva Collins still expects, gets much,” St. Petersburg Times, July 23, 1989, p. 6A; “Pioneering educator does not want post in a Clinton cabinet,” Minneapolis Star Tribune, Oct. 25, 1992, p. 22A.
35 Spitz 1986. See also “Chicago schools get an education in muckraking,” Chicago Tribune, May 8, 1989, p. 1C.
36 “Fairfax principal, 4 other educators disciplined in test-coaching,” Washington Post, Aug. 7, 1987, p. C1.
37 “Pressure for high scores blamed in test cheating,” Los Angeles Times, Sept. 18, 1988, p. 1.
38 “S.I. principal said to fudge school scores,” New York Times, July 19, 1991, p. B1.
39 For a sense of the magnitude of the cheating problem, see “Schools for Scandal,” U.S. News & World Report, April 27, 1992, p. 66.
40 The minister was Luis Alberto Machado, a high official in the ruling party at the time.
41 Based on estimates in the preceding years, the children in the two groups were chosen to be of comparable cognitive ability. For descriptions of the experiment, see Herrnstein et al. 1986; Nickerson 1986.
42 The teachers’ manual for most of the lessons, translated into English, is available as Adams 1986.
43 See Brigham 1932 for the relevant background. Briefly, the SAT was originally designed to be an intelligence test targeted for the college-going population and w
as originally validated against existing intelligence tests. For a modern source showing how carefully the College Board avoids saying the SAT measures intelligence while presenting the evidence that it does, see Donlon 1984.
44 Fallows 1980; Slack and Porter 1980; Messick 1980; DerSimonian and Laird 1983; Dyer 1987; Becker 1990.
45 Messick and Jungeblut 1981.
46 From 1980 to 1992, the SAT-V standard deviation varied from 109 to 112 and the SAT-M standard deviation varied from 117 to 123. For the calculations, we assumed SDs of 110 and 120, respectively.
47 McCall 1979.
48 McCall 1987.
49 Alexander Pope (in his Moral Essays) is the poet, and the entire couplet is “Tis education forms the common mind; / Just as the twig is bent the tree’s inclined.”
50 See Mastropieri 1987 for a review of the expert consensus on this point.
51 For a sympathetic rendition of the program and its history, see Zigler and Muenchow 1992. For a more critical account, see Spitz 1986. We try to keep our account as close to what these two have in common as we can.
The Bell Curve: Intelligence and Class Structure in American Life Page 88