Between- versus within-family factor analyses of cognitive abilities

Confirmatory factor analyses of the 15 cognitive abilities tests from the Hawaii Family Study of Cognition were conducted on between-family (BF) means and within-family (WF) differences for 370 AEA (Americans of European ancestry) and 116 AJA (Americans of Japanese ancestry) sibling pairs. Difference chi-square significance tests, goodness-of-fit indices, and congruence coefficients for the estimated loadings on four specific cognitive abilities factors and on the second-order general intelligence factor nearly all indicated that the between-family factor structures were not significantly different from the within-family structures for both AEA and AJA siblings (the AEA and AJA structures were also not significantly different). The similarity of the BF and WF structures suggests that the genetic and environmental influences underlying cognitive abilities are “intrinsic” in nature, that is, not just due to between-family differences in culture, status, values, and fortuitous cross-assortative mating.     

Cognitive abilities profiles of Caucasian vs Japanese subjects in the Hawaii Family Study of Cognition

General intelligence (the unrotated first principal component) was partialled out of the cognitive abilities factors—verbal ability, spatial ability, perceptual speed, and visual memory—obtained for the 15 tests of cognitive abilities used in the Hawaii Family Study of Cognition (HFSC). The resulting cognitive abilities profiles indicated that HFSC subjects of Caucasian ancestry scored higher relative to subjects of Japanese ancestry on the verbal and visual memory factors, but lower on the spatial and perceptual speed factors. This ethnic group difference in the shape of the cognitive abilities profiles was found to be highly consistent across sexes and generations, in spite of the large mean differences across these groups in factor scores.     

Parent-infant resemblance for general and specific cognitive abilities in the Colorado adoption project

Previous publications emanating from the Colorado Adoption Project have reported significant relationships between parental general cognitive ability (g) and infant Bayley MDI scores. The present study compared infant Bayley factor scores representing separable dimensions of infant cognition with parental general and specific cognitive abilities for 182 adoptive families and 164 nonadoptive families. Parent/offspring correlations between 12-month Bayley factors and parental cognitive abilities suggest only minimal relationships for both parental g and specific abilities. At 24 months, more parent/offspring resemblance was present; moreover, Bayley factors that were related to parental cognition tended to be related to parental g, not to specific abilities. The finding of significant parent/offspring relationships at 24 months between biological parents and their adopted-away infants, as well as between nonadoptive parents and their infants, suggests some genetic continuity from infancy to adulthood.     

Group differences and first principal-component loadings in the Hawaii family study of cognition: a test of the generality of ‘Spearman's hypothesis’

The generality of Spearman's hypothesis that varying differences between whites and blacks on various tests of mental ability are correlated with their g-loadings was tested by analyzing group data from the Hawaii Family Study of Cognition. Data from the three largest ethnic groups tested in the Hawaii Study (Americans of Japanese, Chinese or European ancestry; total N = 5333) were subjected to a principal-component analysis and the first principal component was used as a measure of g. Ethnic group and generation (parent-offspring) differences on 15 tests of specific cognitive abilities were then correlated with their first principal-component loadings. In general, correlations between ethnic group differences and g-loadings are smaller than those recently reported for white-black differences by Jensen (1983); however, those between generation differences and g-loadings are larger. Ethnic group differences on first principal-component scores in the Hawaii Study are less than parent-offspring differences; thus, the correlation between group differences on tests of mental ability and their g-loadings may be a function of the magnitude of the group difference for general mental ability. Because a group difference on g requires group differences on tests which load on g, an observed group difference in general mental ability may necessarily result in a correlation between group differences on individual tests and their g-loadings.     

Estimating the strength of genetic selection against heritable g in a sample of 3520 Americans,sourced from MIDUS II

The relationship between IQ and completed fertility among a sample of 3520 Americans from MIDUS II (1960's birth cohorts) is examined using a common factor comprised of eight cognitive ability measures, in order to determine the rate of phenotypic IQ loss due to genetic selection. Negative correlations are present in both the male and female subsamples, and are associated with a predicted loss in heritable g (g.h) of − .262 points per decade, increasing to − 1.072 points when the additive effect of mutation accumulation is considered. The ability–fertility associations showed Jensen effects at the level of the whole sample (.167), and also separately for each sex (.185 and .147 for the females and males respectively). The magnitude of the expected g.h loss in this cohort due to selection is comparable to that derived from a meta-analysis of disattenuated decadal g.h declines from eight US studies (− .44 points per decade; N = 127,389). There is a Flynn effect in the US amounting to gains of 3.6 points per decade, which are concentrated on more environmentally plastic and specialized sources of ability variance (s.e) suggesting co-occurrent socio-ecological specialization with respect to narrower cognitive abilities in the present cohort.     

Use of factor mixture modeling to capture Spearman's law of diminishing returns

Spearman's law of diminishing returns (SLODR) posits that at higher levels of general cognitive ability the general factor (g) performs less well in explaining individual differences in cognitive test performance. Research has generally supported SLODR, but previous research has required the a priori division of respondents into separate ability or IQ groups. The present study sought to obviate this limitation through the use of factor mixture modeling to investigate SLODR in the Kaufman Assessment Battery for Children-Second Edition (KABC-II). A second-order confirmatory factor model was modeled as a within-class factor structure. The fit and parameter estimates of several models with varying number of classes and factorial invariance restrictions were compared. Given SLODR, a predictable pattern of findings should emerge when factor mixture modeling is applied. Our results were consistent with these SLODR-based predictions, most notably the g factor variance was less in higher g mean classes. Use of factor mixture modeling was found to provide support for SLODR while improving the model used to investigate SLODR.     

Parental ability,education and occupation as influences on offspring cognition in Hawaii and Korea

Partial correlation procedures were used to assess the separate influences of parental ability and parental status (as measured by educational and occupational attainment) on offspring ability, using data acquired from persons of European and Japanese ancestry residing in Hawaii and from Koreans residing in Korea. The magnitudes of the correlations of parental ability and attainment with offspring ability varied substantially across groups. Partial correlations indicate that parent ability and parent status each independently influence offspring performance on measures of cognition, but that the influence of status generally is far weaker than is the influence of parental cognitive ability.     

Measurement Reliability,the Spearman–Jensen Effect and the Revised Thorndike Model of Test Bias

The Thorndike model of test fairness has recently been revised and used to argue that cognitive ability tests are biased against certain groups of test‐takers because ability tests show larger mean differences across racial groups than do job performance measures. We discuss two critical factors that confound this new version of Thorndike's model, making it susceptible to false indications of test bias. Those factors are (a) measurement error (i.e., reliability) in both the predictor and criterion and (b) the Spearman–Jensen effect (i.e., the well‐documented effect that group differences in observed g‐saturated measures are directly proportional to the degree the manifest indicator reflects g). Finally, because the Spearman–Jensen effect is not well known within the applied literature, we present a brief simulation to better elucidate the implications of the Spearman–Jensen effect for personnel selection in general, and claims of bias in cognitive ability testing in particular.     

Expanding the Nexus of Cognitive and Psychomotor Abilities

A study was conducted to expand the nexus of cognitive and psychomotor abilities. A cognitive aptitude battery and a psychomotor battery were administered to 429 military recruits. A confirmatory factor analysis yielded higher-order factors of general cognitive ability (g) and psychomotor/technical knowledge (PM/TK). PM/TK was interpreted as Vernon's (1969) practical factor (k:m). In the joint analysis of these batteries, g and PM/TK each accounted for about 31% of the common variance. No residualized lower-order factor accounted for more than 7% PM/TK influenced a broad range of lower-order psychomotor factors. The first practical implication of these findings is that psychomotor tests are expected to be at least generally interchangeable. A second implication is that the incremental validity of psychomotor tests beyond cognitive tests is expected to be small. These findings should help guide test developers and inform personnel selecting agencies regarding the expected utility of psychomotor tests.     

Psychometric g and mental processing speed on a semantic verification test

The Semantic Verification Test (SVT) consists of brief, simple statements, which are either true or false, about various arrangements of the letters ABC (e.g. B after A). Mean reaction time (RT) for confirming or disconfirming the various statements varies according to their complexity. In independent studies of university students and Navy recruits, RT and other response latency parameters (intraindividual variability and movement time) from SVT performance show significant correlations of about -0.40 with nonspeeded tests of psychometric g. The mean RTs of adults to the various SVT item types are highly related to the mean error rates on these item types when the SVT is taken by elementary school children as a nonspeeded paper-and-pencil test. RT is correlated with the general cognitive ability factor (g) and not with the test-taking speed factor that is found in speeded paper-and-pencil tests. The degree of correlation between RT and psychometric g does not show any regular relationship to differences in the SVT item-type's complexity or difficulty as indicated by mean RT.     

Gray matter correlates of fluid,crystallized, and spatial intelligence: Testing the P-FIT model

The parieto-frontal integration theory (P-FIT) nominates several areas distributed throughout the brain as relevant for intelligence. This theory was derived from previously published studies using a variety of both imaging methods and tests of cognitive ability. Here we test this theory in a new sample of young healthy adults (N = 100) using a psychometric battery tapping fluid, crystallized, and spatial intelligence factors. High resolution structural MRI scans (3T) were obtained and analyzed with Voxel-based Morphometry (VBM). The main findings are consistent with the P-FIT, supporting the view that general intelligence (g) involves multiple cortical areas throughout the brain. Key regions include the dorsolateral prefrontal cortex, Broca's and Wernicke's areas, the somato-sensory association cortex, and the visual association cortex. Further, estimates of crystallized and spatial intelligence with g statistically removed, still share several brain areas with general intelligence, but also show some degree of uniqueness.     

General and Domain-Specific Effectiveness of Cognitive Remediation after Stroke: Systematic Literature Review and Meta-Analysis

Cognitive remediation (CR) has been shown to improve cognitive abilities following a stroke. However, an updated quantitative literature review is needed to synthesize recent research and build understanding of factors that may optimize training parameters and treatment effects. Randomized controlled trials of CR were retrieved from seven electronic databases. Studies specific to adult stroke populations were included. Treatment effects were estimated using a random effects model, with immediate and longer-term follow-up outcomes, and moderator effects, examined for both overall and domain-specific functioning. Twenty-two studies were identified yielding 1098 patients (583 in CR groups). CR produced a small overall effect (g?=?0.48, 95% CI 0.35–0.60, p?<?0.01) compared with control conditions. This effect was moderated by recovery stage (p?<?0.01), study quality (p?=?0.04), and dose (p?=?0.04), but not CR approach (p?=?0.63). Significant small to medium (g?=?0.25–0.75) post-intervention gains were evident within each individual outcome domain examined. A small overall effect (g?=?0.27, 95% CI 0.04–0.51, p?=?0.02) of CR persisted at follow-up (range 2–52 weeks). CR is effective and efficient at improving cognitive performance after stroke. The degree of efficacy varies across cognitive domains, and further high-quality research is required to enhance and sustain the immediate effects. Increased emphasis on early intervention approaches, brain-behavior relationships, and evaluation of activity and participation outcomes is also recommended.     

Associations between cortical thickness and general intelligence in children,adolescents and young adults

Neuroimaging research indicates that human intellectual ability is related to brain structure including the thickness of the cerebral cortex. Most studies indicate that general intelligence is positively associated with cortical thickness in areas of association cortex distributed throughout both brain hemispheres. In this study, we performed a cortical thickness mapping analysis on data from 182 healthy typically developing males and females ages 9 to 24 years to identify correlates of general intelligence (g) scores. To determine if these correlates also mediate associations of specific cognitive abilities with cortical thickness, we regressed specific cognitive test scores on g scores and analyzed the residuals with respect to cortical thickness. The effect of age on the association between cortical thickness and intelligence was examined. We found a widely distributed pattern of positive associations between cortical thickness and g scores, as derived from the first unrotated principal factor of a factor analysis of Wechsler Abbreviated Scale of Intelligence (WASI) subtest scores. After WASI specific cognitive subtest scores were regressed on g factor scores, the residual score variances did not correlate significantly with cortical thickness in the full sample with age covaried. When participants were grouped at the age median, significant positive associations of cortical thickness were obtained in the older group for g-residualized scores on Block Design (a measure of visual-motor integrative processing) while significant negative associations of cortical thickness were observed in the younger group for g-residualized Vocabulary scores. These results regarding correlates of general intelligence are concordant with the existing literature, while the findings from younger versus older subgroups have implications for future research on brain structural correlates of specific cognitive abilities, as well as the cognitive domain specificity of behavioral performance correlates of normative gray matter thinning during adolescence.     

IQ and the wealth of nations: How much reverse causality?

This paper uses data from 130 IQ test administrations worldwide and employs regression analysis to try to quantify the impact of living conditions on average IQ scores in nationally-representative samples. The study emphasizes the possible role of conditions at or near the test-takers' time of birth. The paper finds that the impact of living conditions is of much smaller magnitude than is suggested by just looking at correlations between average IQ scores and socioeconomic indicators. After controlling for test-takers' region of ancestry, the impact of parasitic diseases on average IQ is found to be statistically insignificant when test results from the Caribbean are included in the analysis. As far as IQ and the wealth of nations are concerned, causality thus appears to run mostly from the former to the latter. The test-takers' region of ancestry dominates the regression results. While differences in average scores worldwide can thus be plausibly viewed as being influenced by genetic differences across world regions, it is also possible that score differences are influenced by regional differences in culture that are independent of genetic factors. Differences in average IQ across world regions may change in the years ahead insofar as the strength of Flynn effects may not be uniform, but some regional differences in average g levels seem likely to continue indefinitely.     

How fragile is our intellect? Estimating losses in general intelligence due to both selection and mutation accumulation

Two dysgenic models of declining general intelligence have been proposed. The first posits that since the Industrial Revolution those with low g have had a reproductive advantage over those with high g. The second posits that relaxed purifying selection against deleterious mutations in modern populations has led to g declining due to mutation accumulation. Here, a meta-analytic estimate of the decline due to selection is computed across nine US and UK studies, revealing a loss of .39 points per decade (combined N = 202,924). By combining findings from a high-precision study of the effects of paternal age on offspring g with a study of paternal age and offspring de novo mutation numbers, it is proposed that, 70 de novo mutations per familial generation should reduce offspring g by 2.94 points, or .84 points per decade. Combining the selection and mutation accumulation losses yields a potential overall dysgenic loss of 1.23 points per decade, with upper and lower bound values ranging from 1.92 to .53 points per decade. This estimate is close to those from studies employing the secular slowing of simple reaction time as a potential indicator of declining g, consistent with predictions that mutation accumulation may play a role in these findings.     

Gray matter and intelligence factors: Is there a neuro-g?

Heterogeneous results among neuro-imaging studies using psychometric intelligence measures may result from the variety of tests used. The g-factor may provide a common metric across studies. Here we derived a g-factor from a battery of eight cognitive tests completed by 6929 young adults, 40 of whom also completed structural MRI scans. Regional gray matter (GM) was determined using voxel-based-morphometry (VBM) and correlated to g-scores. Results showed correlations distributed throughout the brain, but there was limited overlap with brain areas identified in a similar study that used a different battery of tests to derive g-scores. Comparable spatial scores (with g variance removed) also were derived from both batteries, and there was considerable overlap in brain areas where GM was correlated to the respective spatial scores. The results indicate that g-scores derived from different test batteries do not necessarily have equivalent neuro-anatomical substrates, suggesting that identifying a “neuro-g” will be difficult. The neuro-anatomical substrate of a spatial factor, however, appears more consistent and implicates a distributed network of brain areas that may be involved with spatial ability. Future imaging studies directed at identifying the neural basis of intelligence may benefit from using a psychometric test battery chosen with specific criteria.     

Combined Medication and CBT for Generalized Anxiety Disorder With African American Participants: Reliability and Validity of Assessments and Preliminary Outcomes

Using data from a study of combined cognitive behavioral therapy (CBT) and venlafaxine XR in the treatment of generalized anxiety disorder (GAD), the current article examines the reliability and convergent validity of scales, and preliminary outcomes, for African American compared with European American patients. Internal consistency and short-term stability coefficients for African Americans (n = 42) were adequate and similar or higher compared with those found for European Americans (n = 164) for standard scales used in GAD treatment research. Correlations among outcome measures among African Americans were in general not significantly different for African Americans compared with European Americans. A subset of patients with DSM-IV–diagnosed GAD (n = 24 African Americans; n = 52 European Americans) were randomly selected to be offered the option of adding 12 sessions of CBT to venlafaxine XR treatment. Of those offered CBT, 33.3% (n = 8) of the African Americans and 32.6% (n = 17) of the European Americans accepted and attended at least one CBT treatment session. The outcomes for African Americans receiving combined treatment were not significantly different from European Americans receiving combined treatment on primary or secondary efficacy measures.     

Raising the IQ: The Ramey and Haskins study

The Ramey and Haskins intervention experiment succeeded in producing IQ gains at three years of age averaging about one standard deviation in young children who were selected for being at risk for subnormal intellectual development. The study is examined in terms of its consistency with other findings, the heritability of IQ, the g aspect of IQ, the simplex pattern of longitudinal interage mental test score correlations, mother-child IQ correlations, and criteria for establishing educationally and socially significant gains in intelligence defined as g rather than as a score on a particular test. Narrow transfer of training from cognitive intervention techniques to IQ test performance in early childhood, rather than enhancement of the g factor itself, is hypothesized as a cause of the typical fadeout of early IQ gains in later childhood.     

Mindfulness induction and cognition: A systematic review and meta-analysis

Mindfulness meditation might improve a variety of cognitive processes, but the available evidence remains fragmented. This preregistered meta-analysis (PROSPERO-CRD42018100320) aimed to provide insight into this hypothesis by assessing the effects of brief mindful attention induction on cognition. Articles were retrieved from Pubmed, PsycInfo and Web of Science up until August 1, 2018. A total of 34 studies were included. The outcomes were categorized into four cognitive domains: attentional functioning, memory, executive functioning and higher-order function. A small effect was found across all cognitive domains (Hedges’ g = 0.18, 95% IC = 0.07–0.29). Separated analyses for each cognitive domain revealed an effect only in higher-order cognitive functions (k = 10, Hedges’ g = 0.35, 95% IC = 0.20–0.50). Results suggest that mindfulness induction improves cognitive performance in tasks involving complex higher-order functions. There was no evidence of publication bias, but studies generally presented many methodological flaws.     

Comparison of black-white differences on the WISC-R and the K-ABC: Spearman's hypothesis

The Kaufman Assessment Battery for Children (K-ABC) and the Wechsler Intelligence Scale for Children-Revise (WISC-R) are compared with respect to the magnitudes of the average white-black differences in standardized scaled scores and in raw scores. The two test batteries were administered to a sample of 172 fourth- and fifth-grade children comprising 86 black-white pairs matched on age, sex, school, and socioeconomic status. The K-ABC and WISC-R are highly correlated, and the general factor, or g, of one battery is virtually identical to the g of the other. The high positive correlation between the size of the white-black difference on the various subtests of both batteries and the subtests' loadings on the g factor bears out Spearman's hypothesis that a test's white-black dicriminability is a direct function of the test's g loading. The lesser white-black discriminability of the K-ABC relative to the WISC-R is attributable to (1) the smaller g loadings of the K-ABC subsets and (2) the presence of other factors, particularly sequential short-term memory which, to some degree, offsets the white-black difference in g.