Controlling for increased guessing enhances the independence of the Flynn effect from g: The return of the Brand effect

Measurement-Invariant Fluid Anti-Flynn Effects in Population-Representative German Student Samples (2012-2022)

Generational IQ test scores in the general population were observed to increase over time (i.e., the Flynn effect) across most of the 1900s. However, according to more recent reports, Flynn effect patterns have seemingly become less consistent. So far, most available evidence on this phenomenon has been categorized by drawing on the classic fluid vs. crystallized intelligence taxonomy. However, recent evidence suggests that subdomain-specific trajectories of IQ change may well be more complex. Here, we present evidence for cross-temporal changes in measurement-invariant figural reasoning tasks in three large-scale, population-representative samples of German secondary school students (total N = 19,474). Analyses revealed a consistent pattern of significant and meaningful declines in performance from 2012 to 2022. Results indicate a decrease in figural reasoning of 4.68 to 5.17 IQ points per decade (corresponding to small-to-medium effects, Cohen ds from 0.34 to 0.38). These findings may be interpreted as tentative evidence for a decreasing strength of the positive manifold of intelligence as a potential cause of the increasing number of recent reports about inconsistent IQ change trajectories.

The Search for the Elusive Basic Processes Underlying Human Intelligence: Historical and Contemporary Perspectives

This article discusses the issues of the basic processes underlying intelligence, considering both historical and contemporary perspectives. The attempt to elucidate basic processes has had, at best, mixed success. There are some problems with pinpointing the underlying basic processes of intelligence, both in theory and as tested, such as what constitutes a basic process, what constitutes intelligence, and whether the processes, basic or not, are the same across time and space (cultural contexts). Nevertheless, the search for basic processes has elucidated phenomena of intelligence that the field would have been hard-pressed to elucidate in any other way. Intelligence cannot be fully understood through any one conceptual or methodological approach. A comprehensive understanding of intelligence requires the converging operations of a variety of approaches to it.

Between-Group Mean Differences in Intelligence in the United States Are >0% Genetically Caused: Five Converging Lines of Evidence

The past 30 years of research in intelligence has produced a wealth of knowledge about the causes and consequences of differences in intelligence between individuals, and today mainstream opinion is that individual differences in intelligence are caused by both genetic and environmental influences. Much more contentious is the discussion over the cause of mean intelligence differences between racial or ethnic groups. In contrast to the general consensus that interindividual differences are both genetic and environmental in origin, some claim that mean intelligence differences between racial groups are completely environmental in origin, whereas others postulate a mix of genetic and environmental causes. In this article I discuss 5 lines of research that provide evidence that mean differences in intelligence between racial and ethnic groups are partially genetic. These lines of evidence are findings in support of Spearman’s hypothesis, consistent results from tests of measurement invariance across American racial groups, the mathematical relationship that exists for between-group and within-group sources of heritability, genomic data derived from genome-wide association studies of intelligence and polygenic scores applied to diverse samples, and admixture studies. I also discuss future potential lines of evidence regarding the causes of average group differences across racial groups. However, the data are not fully conclusive, and the exact degree to which genes influence intergroup mean differences in intelligence is not known. This discussion applies only to native English speakers born in the United States and not necessarily to any other human populations.

Spearman's hypothesis tested comparing Korean young adults with various other groups of young adults on the items of the Advanced Progressive Matrices

Spearman's hypothesis tested at the subtest level of an IQ battery states that differences between races on the subtests of an IQ battery are a function of the g loadings of these subtests, such that there are small differences between races on subtests with low g loadings and large differences between races on subtests with high g loadings. Jensen (1998) stated that Spearman's hypothesis is a law-like phenomenon. It has also been confirmed many times at the level of items of the Raven's Progressive Matrices. This study hypothesizes that with concern to Spearman's hypothesis, subtests and items function in fundamentally the same way, and tested whether Spearman's hypothesis is confirmed at the item level for White-East Asian comparisons. A group of Korean young adults (N=205) was compared with other groups of young adults from Canada, the US, Russia, Peru and South Africa (total N=4770) who took the Advanced Progressive Matrices. Spearman's hypothesis was strongly confirmed with a sample-size-weighted r with a value of 0.63. Computing the g loadings of the items of the Raven with either the Raven-g or the Wechsler-g led to the same conclusions. Tests of Spearman's hypothesis yielded less-strong outcomes when the 36-item Advanced Progressive Matrices were used than when the 60-item Standard Progressive Matrices were used. There is a substantial correlation between sample size and the outcome of Spearman's hypothesis. So, all four hypotheses were confirmed, showing that a part of the subtest-level nomological net replicates at the item level, strengthening the position that, with concern to Spearman's hypothesis, subtests and items function fundamentally the same. It is concluded that Spearman's hypothesis is still a law-like phenomenon. Detailed suggestions for follow-up research are made.

A Meta-Analysis of Spearman’s Hypothesis Tested on Latin-American Hispanics, Including a New Way to Correct for Imperfectly Measuring the Construct of g

Spearman’s hypothesis states that the difference in intelligence between groups is a function of the g loadings of the subtests, where larger differences are found on tests with higher g loadings. This finding has consistently been supported on various groups. In this study we look at samples of Latin-American Hispanics in comparison to Whites. We carried out a meta-analysis based on 14 data points and a total of 16,813 Latin-American Hispanics, including a new way to correct for imperfectly measuring the construct of g. Spearman’s hypothesis was strongly supported with a mean r of 0.63. After correction for various statistical artifacts this value became rho = 0.91. Therefore, we conclude that Spearman’s hypothesis also holds true for White/Latin-American Hispanic differences.

A Meta-Analysis of Spearman’s Hypothesis Tested on Latin-American Hispanics, Including a New Way to Correct for Imperfectly Measuring the Construct of g

Spearman’s hypothesis states that the difference in intelligence between groups is a function of the g loadings of the subtests, where larger differences are found on tests with higher g loadings. This finding has consistently been supported on various groups. In this study we look at samples of Latin-American Hispanics in comparison to Whites. We carried out a meta-analysis based on 14 data points and a total of 16,813 Latin-American Hispanics, including a new way to correct for imperfectly measuring the construct of g. Spearman’s hypothesis was strongly supported with a mean r of 0.63. After correction for various statistical artifacts this value became rho = 0.91. Therefore, we conclude that Spearman’s hypothesis also holds true for White/Latin-American Hispanic differences.

Spearman’s Hypothesis Tested Comparing 47 Regions of Japan Using a Sample of 18 Million Children

Many groups differ in their mean intelligence score. Spearman’s hypothesis states that the differences are a function of cognitive complexity. There tend to be large differences on subtests of high cognitive complexity and small differences on subtests of low cognitive complexity. Spearman’s hypothesis has been supported by a large number of studies. Can Spearman’s hypothesis be generalized to regions of a country, where these regions differ in mean intelligence? We utilized data from 86 different cognitive tests from all 47 Japanese prefectures and correlated the g loadings of 86 subtests with standardized differences on the same subtests. Spearman’s hypothesis was clearly supported: the biggest differences between the regions were on the tests that were of the greatest complexity, meaning that Spearman’s hypothesis may be generalizable from groups to regions. In Japan, g loadings offer a better explanation of group differences in intelligence than cultural differences. Future research should explore whether Spearman’s hypothesis is also supported for differences between regions of other countries.

Spearman’s Hypothesis Tested Comparing 47 Regions of Japan Using a Sample of 18 Million Children

Many groups differ in their mean intelligence score. Spearman’s hypothesis states that the differences are a function of cognitive complexity. There tend to be large differences on subtests of high cognitive complexity and small differences on subtests of low cognitive complexity. Spearman’s hypothesis has been supported by a large number of studies. Can Spearman’s hypothesis be generalized to regions of a country, where these regions differ in mean intelligence? We utilized data from 86 different cognitive tests from all 47 Japanese prefectures and correlated the g loadings of 86 subtests with standardized differences on the same subtests. Spearman’s hypothesis was clearly supported: the biggest differences between the regions were on the tests that were of the greatest complexity, meaning that Spearman’s hypothesis may be generalizable from groups to regions. In Japan, g loadings offer a better explanation of group differences in intelligence than cultural differences. Future research should explore whether Spearman’s hypothesis is also supported for differences between regions of other countries.

One Century of Global IQ Gains: A Formal Meta-Analysis of the Flynn Effect (1909-2013)

The Flynn effect (rising intelligence test performance in the general population over time and generations) varies enigmatically across countries and intelligence domains; its substantive meaning and causes remain elusive. This first formal meta-analysis on the topic revealed worldwide IQ gains across more than one century (1909-2013), based on 271 independent samples, totaling almost 4 million participants, from 31 countries. Key findings include that IQ gains vary according to domain (estimated 0.41, 0.30, 0.28, and 0.21 IQ points annually for fluid, spatial, full-scale, and crystallized IQ test performance, respectively), are stronger for adults than children, and have decreased in more recent decades. Altogether, these findings narrow down proposed theories and candidate factors presumably accounting for the Flynn effect. Factors associated with life history speed seem mainly responsible for the Flynn effect's general trajectory, whereas favorable social multiplier effects and effects related to economic prosperity appear to be responsible for observed differences of the Flynn effect across intelligence domains.

SPEARMAN'S HYPOTHESIS TESTED COMPARING SAUDI ARABIAN CHILDREN AND ADOLESCENTS WITH VARIOUS OTHER GROUPS OF CHILDREN AND ADOLESCENTS ON THE ITEMS OF THE STANDARD PROGRESSIVE MATRICES

Spearman's hypothesis tested at the level of items states that differences between ethnic groups on the items of an IQ test are a function of the g loadings of these items, such that there are small differences between ethnic groups on items with low g loadings and large differences between ethnic groups on items with high g loadings; this has been confirmed in a limited number of studies. In this paper, Spearman's hypothesis was tested, comparing a group of Saudi children and adolescents (N=3209) with other groups of children and adolescents from Denmark, Cyprus, Croatia, Bosnia, South Africa, Estonia, Ukraine, Ireland, Russia and Chile (total N=9333). The analyses were carried out on twelve comparisons between the Saudi Arabian children and the other children. Spearman's hypothesis was confirmed less strongly than in other large-scale studies with a mean weighted r value of 0.44. The relevance of these findings for the discussion on the causes of group differences is discussed.

By their words ye shall know them: Evidence of genetic selection against general intelligence and concurrent environmental enrichment in vocabulary usage since the mid 19th century

It has been theorized that declines in general intelligence (g) due to genetic selection stemming from the inverse association between completed fertility and IQ and the Flynn effect co-occur, with the effects of the latter being concentrated on less heritable non-g sources of intelligence variance. Evidence for this comes from the observation that 19th century populations were more intellectually productive, and also exhibited faster simple reaction times than modern ones, suggesting greater information-processing ability and therefore higher g. This co-occurrence model is tested via examination of historical changes in the utilization frequencies of words from the highly g-loaded WORDSUM test across 5.9 million texts spanning the period 1850-2005. Consistent with predictions, words with higher difficulties (δ parameters from Item Response Theory) and stronger negative correlations between pass rates and completed fertility declined in use over time whereas less difficult and less strongly selected words, increased in use over time, consistent with a Flynn effect stemming in part from the vocabulary enriching effects of increases in population literacy. These findings persisted when explicitly controlled for word age, changing literacy rates and temporal autocorrelation. These trends constitute compelling evidence for the co-occurrence model.