One of the more famous studies on the heritability of IQ is Eric Turkheimer and colleagues’ 2003 paper called Socioeconomic status modifies heritability of IQ in young children. According to Google Scholar, it has been cited more than 700 times. Based on a sample of 7-year-old twins, the study found that in impoverished families the shared environment accounted for about 60 percent of IQ variance while heritability was close to zero. In contrast, heritability was high and the effect of the shared environment nugatory in affluent families.
The literature on the interaction between socioeconomic status and IQ heritability is very mixed. Several studies besides Turkheimer’s find such interaction (although in no other study is it as extreme as in Turkheimer et al. 2003), but others, including some with the very best study designs, find none. I am not going to try to adjudicate between these contradictory findings at this time. Rather, I will show some interesting, hitherto unpublished (well, careful readers of Boetel and Fuerst’s The Nature of Race have seen them already) results pertaining to Turkheimer’s study and the question of race differences. Continue reading
The strong heritability of IQ is well established for white populations in America, with dozens of studies confirming the basic findings. When it comes to heritability in non-whites, the handful of studies that exist (see Jensen 1998, p. 446ff.; Rowe et al. 1999; Guo & Stearns 2002; cf. John’s recent post) do not allow us to conclude that heritability is lower (or higher) in non-white Americans than it is among white Americans, but there is a sore need for more research.
To diminish this uncertainty, we compared the heritability of several different cognitive abilities in whites, blacks, and Hispanics in the CNLSY sample. The sample, which consists of the children of the mothers who are part of the NLSY79 study, includes the results of various ability tests administered between ages 3 and 13. Continue reading
The Commonwealth of Puerto Rico is a Spanish-speaking territory of the United States. Puerto Ricans are United States citizens—they can freely migrate between the island and the states, join the military, or even run for president. But they can’t vote for president, because the territory is not a U.S. state. In three referendums from 1967 to 1998, Puerto Rican voters rejected both political independence and U.S. statehood. However, in November 2012 a solid majority (61.3%) voted in favor of statehood. This kind of political nudging could quite possibly result in Puerto Rico becoming the 51st U.S. state … but only Congress and the president have authority over the matter, and analysts agree that approval is unlikely. This particular referendum also left off the option traditionally most favored by Puerto Ricans: continued commonwealth status. Many islanders appear to feel that statehood offers few additional benefits over citizenship; a majority of Puerto Ricans already live on the U.S. mainland (5 million vs. 3.7 million).
From the earliest days of intelligence testing, social scientists have taken a special interest in U.S. Hispanics. Proportionate to their numbers, it’s possible that more tests have been given to Hispanics than to blacks. But this special attention has also lacked focus. African-American test results have been subject to meticulous cataloging, synthesis and analysis (Shuey, 1966; Jensen, 1998; Jencks & Phillips, 1998) leading to somewhat of a consensus on the size and shape of the black-white cognitive performance gap. Yet there has not been a similar effort to process the disparate and voluminous literature on the abilities of U.S. Hispanics. Therefore there is less knowledge and consensus about the historical and contemporary test performance of Hispanic minorities.
Most of the U.S. Hispanic population is Mexican American (63%). Puerto Ricans are the second largest Hispanic minority (9.2% … or 15.3% including the Commonwealth). This post represents the first effort to comprehensively summarize the abilities of one of these two important American minority groups. Here I describe and analyze the results from over 70 studies that have measured the abilities of Puerto Ricans.
Much has been written about social class differences in the heritability of cognitive ability, little about racial and ethnic differences. I will leave a review of the issue, a discussion of our meta-analytic results, and a report of our technically complex CNLSY ACE x race/ethnicity analysis to my more loquacious (and apt) colleagues. Here I present results based on the (effectively) small NLSY79 kinship sample.
In digit span tests, the respondents are asked to repeat a string of digits. There are two variants of the test, forward digit span (FDS) and backward digit span (BDS). In FDS, the digits are repeated in the order of their presentation, while in BDS they must be repeated in the reverse order. The largest number of digits that a person can repeat without error is his or her forward or backward digit span.
It is well-established that the black-white gap is substantially larger on BDS than FSD (see references in The g Factor by Jensen, p. 405, Note 22; see also my recent analysis of the DAS-II). However, replication is always good, so I analyzed black-white differences in the CNLSY sample, which contains FDS and BDS scores for relatively large samples of black and white children. Additionally, I compared the digit span performance of Hispanic American children to that of blacks and whites. Continue reading
According to Spearman’s hypothesis, the magnitude of the black-white gap on a given cognitive ability test is primarily determined by the test’s g loading. Tests that are better measures of g are associated with larger gaps.
The Differential Ability Scales, Second Edition, or the DAS-II, is an IQ test for assessing children and adolescents. It comprises a total of 21 subtests, although in the present analysis only 13 subtests are used, because not all tests are administered across age groups. I will use the method of correlated vectors (MCV) to test whether g loadings are correlated with mean racial differences on the DAS-II subtests. In addition to the black-white gap, I will also investigate if the test performance of Asians and Hispanics is predicted by g loadings. Continue reading
In the present article, I demonstrate that processing speed (using ASVAB speeded subtests) has a modest predictive validity over the g factor extracted from the ASVAB (non-speeded subtests) in predicting overall GPA in the NLSY97, within black, hispanic and the white sample. Next, I investigate the mediation of speed in the black-white difference in IQ (g). For both analyses, processing speed accounts for a modest portion of these associations. Nonetheless, some issues related with such ‘psychometric speed’ measures need to be clarified.
I present here some more evidence about the race*SES interaction concerning IQ from various survey data. The techniques are employed. Comparison of means among different SES strata, ANCOVA and multiple regression.
While Rushton (1999) demonstrates, using PCA, that g and black-white differences were related, with Flynn Effect (FE) gains over time showing no relationship with the aforementioned variables, Flynn (2000) has challenged Rushton in arguing that Wechsler’s subtest loadings on the Raven test, an universally recognized measure of fluid g, showed positive correlations with both black-white differences and FE gains. Up to now, Flynn’s estimates of g fluid (Gf) has not been scrutinized. I will show presently that the Flynn’s g-fluid (call it, fluid reasoning) and Rushton’s g-crystallized (call it, consolidated knowledge) anomaly was solely due to a single statistical artifact, namely, g_Fluid vector unreliability. By adding additional samples, I created a new, updated Wechsler’s subtest Gf loadings. The present analysis comes to the conclusion that g_Fluid was not in fact correlated with FE gains. Furthermore, this Gf variable has been correlated with other variables as well, such as, heritability (h2), shared environment (c2), nonshared environment (e2), adoption IQ gains, inbreeding depression (ID), and mental retardation (MR). I will also discuss these findings in light of Kan’s (2011) thesis against the hereditarian hypothesis.
In his classic work, Educability and Group Differences, Arthur Jensen presented a number of lines of evidence in defense of his thesis that the Negro-White difference in psychometric intelligence had a congenital component. On the basis of full sibling correlations and relations, Jensen offered the following arguments:
(a1) The full sibling correlations for Blacks and Whites are comparable; (a2) unshared environmental hypotheses, such as nutritional ones, would predict otherwise (pg. 338-339).
(b1) The full sibling correlations for Blacks and Whites are comparable; (b2) a shared environmental hypothesis of group differences would predict otherwise, assuming that the within population heritablities were the same (pg. 108-109).
(c1) The average absolute difference between full siblings is no greater for Blacks than for Whites; (c2) unshared environmental hypotheses, such as nutritional ones, would predict otherwise (pg. 338-339).
(d1) When matching Blacks and Whites on IQ, one sees differential sibling regression, a differential regression which does not decrease with increasing IQ; (d2) an environmental hypothesis of group differences would not predict this (pg. 118-119). Continue reading