Expanding variance and the case of historical changes in IQ means: A critique of Dickens and Flynn (2001).

The Flynn effect is the rise in mean IQ scores during the 20th century, amounting to about 0.33 IQ points per year. Many theoretical explanations have been proposed, though none are universally accepted. W. Dickens and J. R. Flynn's (2001) new approach explains the large IQ changes by means of recursive models of IQ growth. A salient feature of their models is that IQ phenotypes and their supportive environments are correlated; in addition, environmental effects can rebound on phenotypic IQ to increase or lower IQ. In this critique, the authors examine an empirical challenge to their models, which typically imply large changes in IQ variance. However, the historical rise in IQ mean level has not been accompanied by substantial variance changes, a finding inconsistent with the properties of the proposed model. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

"The genetic hypothesis": It was not tested but it could have been.

Comments on the "genetic hypothesis" issue in the U. Neisser et al (see record 83-26553) article, with particular reference to 2 cited studies (J. C. Loehlin et al, see record 51-04436; S. Scarr et al, 1977) which used blood groups to estimate the degree of African ancestry in American Blacks in relation to IQ scores. The methodologies of these studies share the misconception that all blood groups are useful in estimating the proportion of White ancestry in American Blacks. The author argues that this error nullifies the negative finding of the studies, and leaves open the question of whether definitive tests of the genetic hypothesis are possible. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Heterosis doesn't cause the Flynn effect: A critical examination of Mingroni (2007).

Mingroni (see record 2007-10421-011) proposed that heterosis or hybrid vigor may be the principal driver of the Flynn effect—the tendency for IQ scores to increase at a rate of approximately 3 points per decade. This model was presented as a resolution to the IQ paradox—the observation that IQ scores have been increasing despite their high adult heritability—on the basis that substantial changes in IQ can only be accounted for by changes in underlying genetic factors. It is here argued that this model is predicated upon a misconception of the Flynn effect, which is most pronounced on the least g-loaded components of cognitive ability tests and is uncorrelated with genetic effects such as inbreeding depression scores (which are correlated with the g loadings of tests). Evidence supportive of the recently proposed life history model of the Flynn effect is presented. In the discussion, other theoretical objections to the heterosis model are also considered. On this basis, it is concluded that the Flynn effect is strongly entwined with developmental status and that heterosis cannot be its principal cause. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

The heritability of IQ

IQ heritability, the portion of a population's IQ variability attributable to the effects of genes, has been investigated for nearly a century, yet it remains controversial. Covariance between relatives may be due not only to genes, but also to shared environments, and most previous models have assumed different degrees of similarity induced by environments specific to twins, to non-twin siblings (henceforth siblings), and to parents and offspring. We now evaluate an alternative model that replaces these three environments by two maternal womb environments, one for twins and another for siblings, along with a common home environment. Meta-analysis of 212 previous studies shows that our 'maternal-effects' model fits the data better than the 'family-environments' model. Maternal effects, often assumed to be negligible, account for 20% of covariance between twins and 5% between siblings, and the effects of genes are correspondingly reduced, with two measures of heritability being less than 50%. The shared maternal environment may explain the striking correlation between the IQs of twins, especially those of adult twins that were reared apart. IQ heritability increases during early childhood, but whether it stabilizes thereafter remains unclear. A recent study of octogenarians, for instance, suggests that IQ heritability either remains constant through adolescence and adulthood, or continues to increase with age. Although the latter hypothesis has recently been endorsed, it gathers only modest statistical support in our analysis when compared to the maternal-effects hypothesis. Our analysis suggests that it will be important to understand the basis for these maternal effects if ways in which IQ might be increased are to be identified.     

Separation of home intellectual environment and maternal IQ as determinants of child IQ.

Measured both parental and child IQs with the Raven Standard Progressive Matrices and the Peabody Picture Vocabulary Test; Ss included 80 mothers, 35 fathers, and 80 children (mean age 12 yrs). Home intellectual environment was assessed through a 2-hr interview with the mother. Multiple regression analyses showed that for each IQ test and for the 2 scores combined, the addition of home environment ratings to the regression equations did not add a significant increment to the prediction of child IQ from that provided by maternal IQ, whereas the addition of maternal IQ to the regression equation did add a significant increment to that provided by home environment ratings. Thus, the correlation of home environment and child IQ is considerably overestimated when maternal IQ is allowed to covary. When maternal IQ was statistically controlled, the correlation between home environment ratings and child IQ was attenuated to nonsignificance. (13 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dysgenics.

Comments on articles by W. M. Williams and S. J. Ceci (see record 1997-43129-007) and J. C. Loehlin (see record 1997-43129-008) regarding the phenomenon of dysgenics (i.e., the genetic deterioration of the population in regard to intelligence). It is noted that the 2 papers reached different conclusions: Williams and Ceci believe that there is no evidence that dysgenics is present, but Loehlin believes there is such evidence. It is suggested that Williams and Ceci found no evidence because they did not look in the right place for it. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Brain size and intelligence in man: A correction to Peters.

Comments on M. Peters's (see record 1992-18876-001) claim that there is no association between brain size and IQ. It is argued that this claim is incorrect. Studies showing that there is a statistically significant correlation between brain size and IQ are cited. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Auditory inspection time and intelligence: What is the direction of causation?

Inspection time (IT) is an index of speed of perceptual processing that correlates at moderate levels with tests of mental ability. A key issue has been the question of the direction of causation: is IT causal to individual differences in intellectual ability, or is a fast IT a consequence of having a high IQ? The direction of causation was assessed by administering auditory inspection time (AIT) tests and tests of verbal and nonverbal ability to 104 school children at age 11, and 2 years later at 13 years. Three competing structural equation models were tested by using the cross-lagged panel data: that AIT at age 11 causes later IQ; that IQ at age 11 causes later AIT; and that there is equal reciprocal causation. Various goodness-of-fit indexes indicated that the first model was the most acceptable. AIT accounted for about 6% of the variance in cognitive ability 2 years later. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Partialing out intelligence: A methodological and substantive contribution.

Criticizes the use of the partial correlation methodology to control trait variance. It is argued that the only methodology that can be used with fallible measures to control trait variance is factor analysis. In spite of its history of misuse and abuse, the factor methodology can be used objectively and effectively for this purpose. A study by D. J. Satterly (1976) on the relation between cognitive style and intelligence is used as an example of the misuse of factor analysis. However, it is pointed out that when an appropriate factor model is used for Satterly's data, somewhat different interpretations are required. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Familiarity and plausibility in conceptual combination: Reply to Gagné and Spalding (2006).

E. J. Wisniewski and G. L. Murphy (see record 2004-22496-015) suggested that the apparent effects of relation frequency in C. L. Gagné and E. J. Shoben's (1997; see record 1997-02349-004) conceptual combination experiments could be explained by differences between the familiarity and plausibility of their stimuli (noun-noun phrases). However, C. L. Gagné and T. L. Spalding (see record 2006-20573-017) argued that Wisniewski and Murphy's measures of plausibility and frequency are both sensitive to relation frequency. They also suggested that the stimuli were mostly novel, such that differences in familiarity could not explain Gagné and Shoben's findings. The current authors focus on the theoretical rationale for the plausibility and familiarity variables, arguing that the original interpretation of their findings is correct. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Socioeconomic status, IQ, and delinquency.

A number of studies have found a negative relationship between IQ and delinquent involvement. Some researchers maintain that IQ is a spurious variable in the relationship between socioeconomic status (SES) and delinquency, whereas others assert that IQ bears a causal relationship to delinquency that is independent of the effects of SES. Results from 2 Danish prospective longitudinal studies are presented that support the latter view. Ss in the 1st study were 129 males born between September, 1959 and December, 1961; all male offspring born between 1944 and 1947 served as Ss in Study 2 (N?=?31,436). In each study, a significant negative correlation between IQ and level of delinquent involvement remained after SES effects were partialled out. It is posited that low IQ children may be likely to engage in delinquent behavior because their poor verbal abilities limit their opportunities to obtain rewards in the school environment. (34 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Subjective well-being is heritable and genetically correlated with dominance in chimpanzees (Pan troglodytes).

The hypothesis that subjective well-being (SWB) is heritable and genetically correlated with Dominance was tested using 128 zoo chimpanzees. Dominance was a chimpanzee-specific personality factor including items reflecting Extraversion and low Neuroticism. SWB was measured with a 4-item scale. The best behavior genetic model included additive genetic and nonshared environmental effects for SWB and Dominance, marginal maternal effects for SWB, a high genetic correlation, and a low nonshared environmental correlation. Results indicated that the shared variance between SWB and Dominance was a consequence of common genes and that the unique variance between SWB and Dominance was a consequence of the nonshared environment. These findings indicate that common genes may underlie the correlation between human personality factors and SWB. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Flynn effects not genetic and unrelated to race differences.

Comments on the article by J. R. Flynn (see record 1999-00167-001) which argued that massive IQ gains over time test the IQ-intelligence equation, reveal groups who achieve far beyond their mean IQ's and falsify prominent arguments for a genetic racial IQ gap. The author contends that Flynn fails to report in sufficient detail a summary of what the gains over time do and do not tell us about the nature of the Black–White difference. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Heritability estimates versus large environmental effects: The IQ paradox resolved.

Some argue that the high heritability of IQ renders purely environmental explanations for large IQ differences between groups implausible. Yet, large environmentally induced IQ gains between generations suggest an important role for environment in shaping IQ. The authors present a formal model of the process determining IQ in which people's IQs are affected by both environment and genes, but in which their environments are matched to their IQs. The authors show how such a model allows very large effects for environment, even incorporating the highest estimates of heritability. Besides resolving the paradox, the authors show that the model can account for a number of other phenomena, some of which are anomalous when viewed from the standard perspective. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

On Hebb's criticism of Jensen.

Notes that D. O. Hebb's (see record 1990-56823-001) criticism of A. R. Jensen's (1969) consideration of the contributions of environment vs heredity to IQ is based on a failure to distinguish between the variance within a particular group and the variance between groups. Use of a one-group analysis cannot show the effects or importance of a factor in determining an aspect of behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Multiplicative validity generalization model: Accuracy of estimates as a function of sample size and mean, variance, and shape of distribution of true validities.

Used simulation techniques to study the accuracy of estimates of the mean, variance, and lower credibility value of true validities produced by the independent multiplicative model and by a modified dependent model that takes the correlation between range restriction and criterion reliability artifacts into account. Sample sizes (n?=?50 or 100) and the number of studies/analyses (50) were selected to be consistent with the typical parameters found in 129 validity generalization analyses. The mean, standard deviation, and shape of the true validity distributions were systematically varied. It is concluded that the independent and modified dependent estimates were typically accurate, although the credibility estimates were affected by the extremely skewed distributions. The mean and variance estimates from both models were not affected by distribution shape. Results support the applicability of the 1st 2 authors' (see record 1981-27033-001) models and F. L. Schmidt and J. E. Hunter's (see record 1978-11448-001) noninteractive model. Some limitations of the "bare-bones" sampling-error-only approach are noted. (9 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A test of J. R. Harris's theory of peer influences on personality.

J. R. Harris's (1995) theory that peer influence plays a central role in shaping personality was tested from the data of the National Merit twin study (J. C. Loehlin & R. C. Nichols, 1976), by examining whether members of 839 late-adolescent twin pairs who shared more friends were more similar in personality than those who shared fewer friends. Ambiguity regarding the direction of effects was partially controlled by comparing monozygotic and dizygotic twin pairs. Comparisons were made between the effect of peer overlap and similarity of parental treatment. These were made both for personality traits, as measured by the California Psychological Inventory, and for academic achievement, as measured by the subscale and total scores of the National Merit Scholarship Qualifying Test. A number of the results were consistent with Harris's theory, although quantitatively the effects were not strong. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Delinquency and impulsivity and IQ: A reply to Block (1995).

Although J. Block's critique (see record 1995-29649-001) of the D. Lynam, T. Moffitt, and M. Stouthamer-Loeber report (see record 1993-29924-001) contains several interesting points, many of his criticisms are not valid and resulted from miscommunications, misunderstandings, and simple preferences. Specifically, the authors believe the criticisms to be the results of mistaking a single hypothesis for an organizing principle, a misunderstanding of the reported path analyses, and a simple preference for impulsivity over IQ as an explanatory construct. An attempt is made to address the misinterpretation through clarification of the predicted relations between IQ, executive dysfunction, impulsivity, and delinquency. The original path analyses are reviewed and are shown to refute not only the original self-control hypothesis (Lynam et al., 1993), as reported, but also Block's more recent version. Finally, evidence marshalled by Block to support his emphasis on impulsive personality over low IQ is argued to have inadequacies from empirical and social policy perspectives. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Is the evidence on ethnicity and intelligence conclusive?

Comments on an article by R. L. Sternberg, E. L. Grigorenko, and K. K. Kidd (see record 2005-00117-006). While praising the Sternberg et al. article, the present author has a couple of concerns. One is that the authors imply that the question of whether the Black-White IQ discrepancy has a genetic component should be a closed issue. I maintain that no argument should be regarded as a closed one when there are so many psychologists on both sides of a scientific position. In light of a study by M. Snyderman & S. Rothman (1988) the fact that 24% of the experts surveyed expressed uncertainty in this matter means that more research and dialogue rather than a "case closed" orientation is needed. My second concern is that of the insufficient respect given to the work of J. P. Rushton (1995), who contended that greater intelligence evolved in colder climates because of the greater difficulty in obtaining food and protection from the elements. Sternberg et al. (2005) maintained that Rushton's position has no more merit than contending that greater intelligence evolved in tropical climates because of the need to cope with tropical diseases and the violence associated with hot weather. Rushton presented a vast array of scientific evidence in his conceptualization, for example, a correlation of .62 between cranial capacity and distance from the equator with 20,000 crania representing 122 ethnically distinguishable populations (K. L. Beals, C. L. Smith, & S. M. Dodd, 1984). D. I. Templer and H. Arikawa (2003) reported a correlation of -.71 between mean IQ and mean high winter temperature and a correlation of -.61 between mean IQ and mean low winter temperature with 129 countries. There are alternative explanations to those of Rushton for such findings. To relegate Rushton's theory to the realm of absurdity, however, would neither constitute optimal scientific reasoning nor represent an ideal spirit of scholarly disagreement. (PsycINFO Database Record (c) 2010 APA, all rights reserved)