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

Special Series on the Wechsler Adult Intelligence Scale-IV Performances in Five Asian Countries: Summary of Findings, Clinical Implications, and Future Directions

INTRODUCTION

This special series of exploratory studies compared WAIS-IV performances in five Asian countries: Japan, South Korea, Taiwan, India, and Indonesia with the U.S. The studies examined cognitive profiles across age groups to develop hypotheses on how culture can impact cognition. This summary article integrates the findings from each study to determine similarities and differences across Asian countries and proposes possible underlying cultural factors impacting cognition.

METHODS

In each study, raw scores corresponding to a subscale score of 10 were scored with U.S. norms across all age groups. Index scores were calculated with the adjusted scale scores. The impact of education on test performances was determined by correlating WAIS-IV scores with a ratio of educational attainment for each country with the U.S. for each age group. Findings from each country were then integrated to develop hypotheses on cultural factors that impacted cognitive profiles.

RESULTS

East Asian countries (Japan, South Korea, Taiwan) demonstrated weaker Verbal Comprehension Index scores and stronger Processing Speed Index scores than the U.S. sample, although the latter was moderated by age. East Asian countries demonstrated stronger performances on Perceptual Reasoning versus Verbal Comprehension tests. East Asians and the Java subset of the Indonesian sample demonstrated a pattern of stronger performances in younger versus older cohorts which was significantly correlated with educational attainment.

DISCUSSION

Cultural factors impacting cognition were proposed. Clinical implications of the findings were discussed and directions for future studies to examine the relationship between culture and cognition were recommended.

The FinSwed study: Using verbal NEPSY-II subtests with a cultural minority group

While it has been established that cultural differences in test performance are common, few studies have compared groups from different countries that speak the same language. The aim of this study was to investigate the generalizability of selected linguistic and verbal memory subtests from the Swedish NEPSY-II to the Finland-Swedish minority group. The participants were 275 Swedish-speaking children from Finland aged 5-16-years. The performance was compared to the U.S. norms used in the test. The Finland-Swedish children scored around scaled score 12 and significantly higher than the normative mean on the subtests Comprehension of Instructions, Phonological Processing, Word Generation Semantic, List Memory, and Sentence Repetition, whereas no significant differences to the norms emerged for the subtests Word Generation Initial Letter, Narrative Memory, and Word List Interference. There was a significant age effect for two subtests, with scaled scores increasing with age. Lower parental education and male sex were associated with lower test scores on some subtests, whereas bilingualism was not. The findings were viewed in relation to previous comparison studies involving the NEPSY-II/NEPSY. The differences were suggested to relate to cultural, educational, and test-related differences between Finland, Sweden, and the U.S. The results add to the clinical utility of the NEPSY-II.

New Evidence of Healthier Aging: Positive Cohort Effects on Verbal Fluency

Background and Objectives

Cross-sectional studies have shown improvements in cognition in later-born cohorts. However, it remains unclear whether these cohort effects extend beyond cognitive levels and are also detectable in the rate of age-related cognitive decline. Additionally, evidence is scarce on the presence and consistency of cohort effects throughout different segments of the distribution of cognitive trajectories.

Research Design and Methods

This study evaluates the existence and variability of cohort effects across the entire distribution of aging-related trajectories of verbal fluency. With this purpose, we develop sex and education-adjusted longitudinal norms of verbal fluency using data from 9 waves of the English Longitudinal Study of Aging (ELSA) by fitting quantile mixed models. The effect of age was modeled using splines to assess birth cohort effects, after grouping individuals in 5-year groups from 1920 to 1950 according to their age at study entry. To test for possible cohort effects across the 10th, 50th, and 90th quantiles, the coefficients associated with the splines were allowed to vary among cohorts.

Results

Our results suggest that, consistently across longitudinal quantiles, decline in verbal fluency across age is less pronounced for later-born individuals (p < .001), supporting the hypothesis of cohort effects. Additionally, we also found that quantiles of verbal fluency at any age are shifted upwards in later-born cohorts compared to those in earlier-born cohorts.

Discussion and Implications

These results enhance our understanding of cognitive decline in older adults by demonstrating that cohort effects on cognition are observable both cross-sectionally and longitudinally, affecting the entire range of verbal fluency trajectories.

Questioning cognitive heterogeneity and intellectual functioning in fetal alcohol spectrum disorders from the Wechsler Intelligence Scale for Children

Introduction: Fetal Alcohol Spectrum Disorders (FASD) are characterized by a variety of multiple cognitive and behavioral impairments, with intellectual, attentional, and executive impairments being the most commonly reported. In populations with multiple neurodevelopmental disorders, the Full Scale Intelligence Quotient (FSIQ) may not be a proper measure of intellectual abilities, rarely interpreted in FASD clinical practice because the heterogeneity of the cognitive profile is deemed too strong. We propose a quantitative characterization of this heterogeneity, of the strengths and weaknesses profile, and a differential analysis between global cognitive (FSIQ) and elementary reasoning abilities in a large retrospective monocentric FASD sample. Methods: Using clinical and cognitive data (Wechsler Intelligence Scale for Children) from 107 children with FASD, we characterized subject heterogeneity (variance and scatter of scaled/composite scores), searched for strengths and weaknesses, and specified intellectual functioning in terms of FSIQ and elementary reasoning (General Abilities Index, Highest Reasoning Scaled Score), in comparison with standardization norms and a Monte-Carlo-simulated sample from normalization data. Results: Performance of children with FASD was lower on all subtests, with a significant weakness in working memory and processing speed. We found no increase in the variance and scatter of the scores, but a discordance between the assessment of global cognitive functioning (28% borderline, 23% deficient) and that of global and elementary reasoning abilities (23-9% borderline, 15-14% deficient). Conclusion: Our results question the notion of WISC profile heterogeneity in FASD and point to working memory and processing speed over-impairment, with global repercussions but most often preserved elementary reasoning abilities.

Adolescent Nonsuicidal Self-Injury and Suicidality: A Latent Class Analysis and Associations with Clinical Characteristics in an At-Risk Cohort

Nonsuicidal self-injury (NSSI) is frequently encountered in adolescents, but its predictive value for suicidality or other clinical characteristics is challenging due to its heterogeneous nature. This study used latent class analysis to identify subgroups of NSSI and compared these on sociodemographic characteristics, adverse outcomes and protective factors. The study included 966 high-risk adolescents, Mage 14.9 y, SD 0.9 y, 51.8% female. Four classes emerged: (1) "Low NSSI-Low suicidality", (2) "Moderate NSSI-Low suicidality", (3) "Moderate NSSI-High suicidality", and (4) "High NSSI-High suicidality". Girls predominated in the high suicidality classes. Generally, Class 4 had the poorest outcomes: more internalizing and externalizing problems, less social support from friends and families and worst self-esteem. These findings emphasize the need for interventions tailored to specific phenotypes of adolescents engaging in NSSI.

Secular trends in physical growth, biological maturation, and intelligence in children and adolescents born between 1978 and 1993

Introduction

Human physical growth, biological maturation, and intelligence have been documented as increasing for over 100 years. Comparing the timing of secular trends in these characteristics could provide insight into what underlies them. However, they have not been examined in parallel in the same cohort during different developmental phases. Thus, the aim of this study was to examine secular trends in body height, weight, and head circumference, biological maturation, and intelligence by assessing these traits concurrently at four points during development: the ages of 4, 9, 14, and 18 years.

Methods

Data derived from growth measures, bone age as an indicator of biological maturation, and full-scale intelligence tests were drawn from 236 participants of the Zurich Longitudinal Studies born between 1978 and 1993. In addition, birth weight was analyzed as an indicator of prenatal conditions.

Results

Secular trends for height and weight at 4 years were positive (0.35 SD increase per decade for height and an insignificant 0.27 SD increase per decade for weight) and remained similar at 9 and 14 years (height: 0.46 SD and 0.38 SD increase per decade; weight: 0.51 SD and 0.51 SD increase per decade, respectively) as well as for weight at age 18 years (0.36 SD increase per decade). In contrast, the secular trend in height was no longer evident at age 18 years (0.09 SD increase per decade). Secular trends for biological maturation at 14 years were similar to those of height and weight (0.54 SD increase per decade). At 18 years, the trend was non-significant (0.38 SD increase per decade). For intelligence, a positive secular trend was found at 4 years (0.54 SD increase per decade). In contrast, negative secular trends were observed at 9 years (0.54 SD decrease per decade) and 14 years (0.60 SD decrease per decade). No secular trend was observed at any of the four ages for head circumference (0.01, 0.24, 0.17, and - 0.04 SD increase per decade, respectively) and birth weight (0.01 SD decrease per decade).

Discussion

The different patterns of changes in physical growth, biological maturation, and intelligence between 1978 and 1993 indicate that distinct mechanisms underlie these secular trends.

Generalizability of the Swedish WISC-V to the Finland-Swedish minority - the FinSwed study

International guidelines highlight the importance of using appropriate and culturally fair test materials when conducting clinical psychological assessments. In the present study, the generalizability of the Swedish WISC-V with Scandinavian normative data was explored in 6-16-year-old Swedish-speaking children in Finland (N = 134), as no local test versions or norms are available for this minority. First, metric measurement invariance was established, i.e., the constructs measured were equivalent between the standardization data and the present sample. Second, the performance of this minority group on the Swedish WISC-V was compared to the Scandinavian normative mean. The findings showed that the Finland-Swedish children performed overall higher than the normative mean on the Swedish WISC-V, with an FSIQ of 103. The performance was significantly higher also in the indexes VSI, FRI, and WMI as well as in several subtests. However, in the subtest Vocabulary, the Finland-Swedish children achieved significantly lower scores than the Scandinavian mean. Further analyses showed significant associations between cognitive performance and age as well as parental education. For the VCI and the FSIQ, performance increased significantly with age, despite the use of age-standardized scaled scores. The general high performance was suggested to relate to the overall high educational level of the Finland-Swedes as well as to other cultural and test-related factors. The results have implications for clinicians conducting assessments with this minority, but also highlight the importance of establishing test fairness by validating tests when used in different cultural groups.

Stability of developmental milestones: Insights from a 44-year analysis

Using standardized test procedures is a reliable way of assessing early childhood development in the pediatric setting. However, normal population's developmental parameters may change over time. The aim of this study was to determine whether a change of developmental percentiles is present in infants in Germany during recent decades. Measured by an established German diagnostic instrument (Münchener Funktionelle Entwicklungsdiagnostik) we cross-sectionally compared developmental data (cognition, expressive language, language comprehension, fine and gross motor skills, social development, daily-living skills) of children aged 0-36 months collected in the 1970s and in 2018. N = 2065 children and their parents were included (1970s sample: N = 1660 and 2018 sample: N = 405). The T-Test of dependent variables showed nonsignificant differences in the developmental scales. We hypothesized an infant Flynn effect, but the results of this study suggest that there are no developmental changes associated with the 50th percentile. Nevertheless, it is critical to emphasize the need for periodic revision and re-norming of developmental test procedures, even in the absence of significant changes in individual items.

Investigating changes in IQ scores over a decade in Brazil: factors at play

PURPOSE

This study aimed to determine whether the factors underlying potential differences between two birth cohorts, born in 1982 and 1993, influence the changes in IQ over time.

METHODS

Data from two Brazilian birth cohorts were used (1993 and 1982 Pelotas Birth Cohorts). The IQ scores were assessed using the WAIS-III test.

RESULTS

Results showed that women born in 1993 had a higher average IQ score than those born in 1982, but no difference was found among men. The increase in IQ scores was only limited to participants from families with an income ranging from 1.1 to 3 times the minimum wage at the time of birth. The mean IQ score of participants born to mothers below the age of 20 remained stable over time, but increase for participants whose mothers were 20 years of age or older at the time of birth.

CONCLUSIONS

This study emphasizes the importance of considering socio-economic and demographic factors when examining differences in IQ scores over time. Further research is needed to understand the underlying mechanisms of these findings.

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.

A Systematic Review and New Analyses of the Gender-Equality Paradox

Some studies show that living conditions, such as economy, gender equality, and education, are associated with the magnitude of psychological sex differences. We systematically and quantitatively reviewed 54 articles and conducted new analyses on 27 meta-analyses and large-scale studies to investigate the association between living conditions and psychological sex differences. We found that sex differences in personality, verbal abilities, episodic memory, and negative emotions are more pronounced in countries with higher living conditions. In contrast, sex differences in sexual behavior, partner preferences, and math are smaller in countries with higher living conditions. We also observed that economic indicators of living conditions, such as gross domestic product, are most sensitive in predicting the magnitude of sex differences. Taken together, results indicate that more sex differences are larger, rather than smaller, in countries with higher living conditions. It should therefore be expected that the magnitude of most psychological sex differences will remain unchanged or become more pronounced with improvements in living conditions, such as economy, gender equality, and education.

Assessment of Specific Learning Disabilities and Intellectual Disabilities

We review literature related to the assessment and identification of Specific Learning Disabilities (SLD) and Intellectual Disabilities (ID). SLD and ID are the only two disorders requiring psychometric test performance for identification within the group of neurodevelopmental disorders in Diagnostic and Statistical Manual - 5. SLD and ID are considered exclusionary of one another, but the processes for assessment and identification of each disorder vary. There is controversy about the identification and assessment methods for SLD, with little consensus. Unlike ID, SLD is weakly related to full-scale IQ, and there is insufficient evidence that the routine assessment of IQ or cognitive skills adds value to SLD identification and treatment. We have proposed a hybrid method based on the assessment of low achievement with norm-referenced tests, instructional response, and other disorders and contextual factors that may be comorbid or contraindicative of SLD. In contrast to SLD, there is strong consensus for a three-prong definition for the identification and assessment of ID: (a) significantly subaverage IQ, (b) adaptive behavior deficits that interfere with independent living in the community, and (c) age of onset in the developmental period. For both SLD and ID, we identify areas of controversy and best practices for identification and assessment.

Cognitive performance outcomes: considerations for drug development

Ensuring that cognitive assessments are fit for purpose is critical in the evaluation of the clinical benefit of new therapeutic interventions. Although guidelines for Clinical Outcome Assessments (COA) are available, performance outcome (PerfO) assessments, and in particular those assessing cognition (Cog-PerfOs) are more complex and have additional requirements that need to be considered. I outline three areas where further discussion around validation methods for Cog-PerfOs and best practices is warranted: (1) content validity (2) ecological validity, and (3) construct validity in multinational contexts. I conclude with a discussion of several potential avenues for the improvement of validation of Cog-PerfOs used to evaluate the efficacy of medical products that target cognitive symptomatology. These include the involvement of cognitive psychologists in establishing content validity of Cog-PerfOs, evaluating the congruence of laypeople's and expert understanding of cognitive concepts, supplementing qualitative with quantitative evidence when establishing content validity, demonstrating ecological validity, and ensuring normative data are available in multinational contexts.

Weakening of the cognition and height association from 1957 to 2018: Findings from four British birth cohort studies

Background

Taller individuals have been repeatedly found to have higher scores on cognitive assessments. Recent studies have suggested that this association can be explained by genetic factors, yet this does not preclude the influence of environmental or social factors that may change over time. We thus tested whether the association changed across time using data from four British birth cohorts (born in 1946, 1958, 1970, and 2001).

Methods

In each cohort height was measured and cognition via verbal reasoning, vocabulary/comprehension, and mathematical tests; at ages 10/11 and 14/17 years (N=41,418). We examined associations between height and cognition at each age, separately in each cohort, and for each cognitive test administered. Linear and quantile regression models were used.

Results

Taller participants had higher mean cognitive assessment scores in childhood and adolescence, yet the associations were weaker in later (1970 and 2001) cohorts. For example, the mean difference in height comparing the highest with lowest verbal cognition scores at 10/11 years was 0.57 SD (95% CI = 0.44-0.70) in the 1946 cohort, yet 0.30 SD (0.23-0.37) in the 2001 cohort. Expressed alternatively, there was a reduction in correlation from 0.17 (0.15-0.20) to 0.08 (0.06-0.10). This pattern of change in the association was observed across all ages and cognition measures used, was robust to adjustment for social class and parental height, and modeling of plausible missing-not-at-random scenarios. Quantile regression analyses suggested that these differences were driven by differences in the lower centiles of height, where environmental influence may be greatest.

Conclusions

Associations between height and cognitive assessment scores in childhood-adolescence substantially weakened from 1957-2018. These results support the notion that environmental and social change can markedly weaken associations between cognition and other traits.

Funding

DB is supported by the Economic and Social Research Council (grant number ES/M001660/1); DB and LW by the Medical Research Council (MR/V002147/1). The Medical Research Council (MRC) and the University of Bristol support the MRC Integrative Epidemiology Unit [MC_UU_00011/1]. NMD is supported by an Norwegian Research Council Grant number 295989. VM is supported by the CLOSER Innovation Fund WP19 which is funded by the Economic and Social Research Council (award reference: ES/K000357/1) and Economic and Social Research Council (ES/M001660/1). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Secular trends in motor performance in Swiss children and adolescents from 1983 to 2018

Introduction

Environmental changes, including globalization, urbanization, social and cultural changes in society, and exposure to modern digital technology undoubtedly have an impact on children’s activity and lifestyle behavior. In fact, marked reductions in children’s physical activity levels have been reported over the years and sedentary behavior has increased around the world. The question arises whether these environmental changes had an impact on general motor performance in children and adolescents. The study aimed to investigate secular trends of motor performance in Swiss children and adolescents, aged between 7 and 18 years, over a period of 35 years from 1983 to 2018.

Methods

Longitudinal data on the five motor components of the Zurich Neuromotor Assessment (ZNA) – pure motor (PM), fine motor (FM), dynamic balance (DB), static balance (SB), and contralateral associated movements (CAM) – were pooled with cross-sectional data on PM and FM from eight ZNA studies between 1983 and 2018. Regression models were used to estimate the effect of the year of birth on motor performance and body mass index (BMI) measurements. Models were adjusted for age, sex, and socioeconomic status.

Results

The secular trend estimates in standard deviation scores (SDS) per 10 years were − 0.06 [−0.33; 0.22, 95% Confidence Interval] for PM, −0.11 [−0.41; 0.20] for FM, −0.38 [−0.66; −0.09] for DB (−0.42 when controlled for BMI), −0.21 [−0.47; 0.06] for SB, and − 0.01 [−0.32; 0.31] for CAM. The mean change in BMI data was positive with 0.30 SDS [0.07; 0.53] over 10 years.

Discussion

Despite substantial societal changes since the 1980s, motor performance has remained relatively stable across generations. No secular trend was found in FM, PM, SB, and CAM over a period of 35 years. A secular trend in DB was present independent of the secular trend in body mass index.

It Runs in the Family: Testing for Longitudinal Family Flynn Effects

The Flynn effect refers to increases over time in measured (particularly fluid) intelligence of approximately 3 IQ points per decade. We define the Flynn effect at the family level, using longitudinal data and two new family-level cohort definitions. Multilevel growth curve analyses of the National Longitudinal Survey of Youth 1979 data showed that children in families with later-born mothers had higher average PIAT math scores, and lower average reading comprehension scores and growth, in young and middle childhood. Children in families where the first child was born later had higher average PIAT math, reading recognition, and reading comprehension scores, as well as larger developmental growth. The latter family-level Flynn effects were of higher magnitudes than the usual individual-level Flynn effect found in previous studies. Our results, showing family level-intercept and slope Flynn effects for both maternal birthyear and first child birthyear, have implications for research aiming to explain the Flynn effect.

Students' intelligence test results after six and sixteen months of irregular schooling due to the COVID-19 pandemic

The COVID-19 pandemic has affected schooling worldwide. In many places, schools closed for weeks or months, only part of the student body could be educated at any one time, or students were taught online. Previous research discloses the relevance of schooling for the development of cognitive abilities. We therefore compared the intelligence test performance of 424 German secondary school students in Grades 7 to 9 (42% female) tested after the first six months of the COVID-19 pandemic (i.e., 2020 sample) to the results of two highly comparable student samples tested in 2002 (n = 1506) and 2012 (n = 197). The results revealed substantially and significantly lower intelligence test scores in the 2020 sample than in both the 2002 and 2012 samples. We retested the 2020 sample after another full school year of COVID-19-affected schooling in 2021. We found mean-level changes of typical magnitude, with no signs of catching up to previous cohorts or further declines in cognitive performance. Perceived stress during the pandemic did not affect changes in intelligence test results between the two measurements.

Today's Older Adults Are Cognitively Fitter Than Older Adults Were 20 Years Ago, but When and How They Decline Is No Different Than in the Past

History-graded increases in older adults' levels of cognitive performance are well documented, but little is known about historical shifts in within-person change: cognitive decline and onset of decline. We combined harmonized perceptual-motor speed data from independent samples recruited in 1990 and 2010 to obtain 2,008 age-matched longitudinal observations (M = 78 years, 50% women) from 228 participants in the Berlin Aging Study (BASE) and 583 participants in the Berlin Aging Study II (BASE-II). We used nonlinear growth models that orthogonalized within- and between-person age effects and controlled for retest effects. At age 78, the later-born BASE-II cohort substantially outperformed the earlier-born BASE cohort (d = 1.20; 25 years of age difference). Age trajectories, however, were parallel, and there was no evidence of cohort differences in the amount or rate of decline and the onset of decline. Cognitive functioning has shifted to higher levels, but cognitive decline in old age appears to proceed similarly as it did two decades ago.

Neurodiversity and Intelligence: Evaluating the Flynn Effect in Children with Autism Spectrum Disorder

The Flynn Effect (FE) among child and adolescent populations indicates that intelligence scores improve by about three points per decade. Using nine years of data from the National Database for Autism Research, this study examined whether general intelligence changed significantly for nine cohorts with autism spectrum disorder (ASD; N = 671). Analyses demonstrated a downward trend such that Cohen's d from 1998 to 2006 was - 0.27. The mean IQ is 92.74 for years 1-3, 91.54 for years 4-6, and 87.34 for years 7-9, indicating a reverse FE of 5.4 points per decade. A linear regression revealed a significant negative FE comparable to the positive effect of age on IQ among those with ASD. Implications for research, practice, and law are discussed.

Comparison of WPPSI-IV and WISC-V cognitive profiles in 6-7-year-old Finland-Swedish children - findings from the FinSwed study

The Wechsler scales are among the most widely used tests in cognitive and neuropsychological assessments. When assessing children aged 6:0-7:7 years the clinician can choose between Wechsler Preschool and Primary Scale of Intelligence - Fourth Edition (WPPSI-IV) and Wechsler Intelligence Scale for Children - Fifth Edition (WISC-V). Information about how the tests function and differ in this overlapping age range is limited. Using a between-subjects design, the present study compared the cognitive profiles of typically developing Swedish-speaking children in Finland in this overlapping age range (6:1 - 7:2 years), assessed with the Swedish versions of either WPPSI-IV (n = 38) or WISC-V (n = 24). Profile analyses and one-way ANCOVA were performed to investigate differences in the comparable subtests, indexes and Full Scale IQ. On the subtest level, children assessed with WISC-V had significantly lower scores on the subtests Vocabulary, Matrix Reasoning, and Bug/Symbol Search compared to children assessed with WPPSI-IV. On the index level, scores for the Verbal Comprehension Index and the Fluid Reasoning Index were significantly lower for children assessed with WISC-V. The Full Scale IQ was significantly lower on WISC-V. Taken together, the findings indicate that WPPSI-IV and WISC-V produce partly different cognitive profiles. These differences are important to recognize when choosing which test to use and when interpreting the results of clinical assessments of children in this age group.

Intelligenzsteigerung durch Neuroenhancement?

Zusammenfassung. Die menschliche Intelligenz gehört zu den bestuntersuchten psychologischen Merkmalen, in denen interindividuelle Differenzen bestehen. Die mehr als 100jährige Forschungsgeschichte hat einen hoch belastbaren Wissensstand hervorgebracht; dieser umfasst die Definition, die Psychometrie, die (ontogenetische) Entwicklung, die Struktur, die Vorhersagekraft für real-life-Variablen, das Wissen über elementar-kognitive, verhaltensgenetische und neurobiologische Grundlagen der Intelligenz, u.v.m. Jüngst steht zudem die Frage des ‚enhancements‘ der Intelligenz im Fokus, eine Frage, die nicht zuletzt durch die aktuelle philosophische Strömung des Transhumanismus stark an Bedeutung gewinnt. Der Transhumanismus nimmt eine substanzielle Erhöhung (enhancement) von Fähigkeiten und anderen (auch) psychologischen Eigenschaften des Menschen ins Zentrum und postuliert, dass ein soziokultureller Fortschritt – und letztlich das Überlegen des Homo Sapiens und unseres Planeten – erst durch technologischen Fortschritt ermöglicht werde. Viele Transhumanisten stellen eine substanzielle Steigerung der Intelligenz in den Vordergrund, die primär durch (neuro–)‌technologische und pharmakologische Maßnahmen zu bewerkstelligen seien. Diese Debatten sind jedoch oft gekennzeichnet durch übertrieben optimistische Annahmen der Möglichkeiten moderner neurowissenschaftlicher Methoden bei gleichzeitiger Vernachlässigung der potenziellen negativen Folgen für das Individuum, für die Gesellschaften und insgesamt für unsere Spezies. Im gegenständlichen Überblicksbeitrag werden behaviorale, neuroelektrische und pharmakologische Methoden im Hinblick auf ihr aktuelles Potenzial einer Steigerung der individuellen Intelligenz analysiert. Die zwischenzeitlich zu diesen Fragen vorliegenden experimentellen Studien, sowie verfügbare Metaanalysen lassen allerdings den Schluss zu, dass bislang keine der gegenwärtig verfügbaren Methoden das Potenzial haben, die individuelle Intelligenz substanziell zu steigern. Und selbst falls solche möglicherweise in absehbarer Zeit zur Verfügung stünden, müssen zuvor sowohl individuelle als auch gesellschaftliche (negative) Konsequenzen einer kritischen Analyse unterzogen werden. Diese sind Gegenstand einer abschließenden Diskussion.

The role of school education in time-dependent changes of cognitive abilities in cohorts from midlife to old age

OBJECTIVES

It is examined whether older adults' cognitive ability in terms of delayed recall and verbal fluency is improving over time, whether this occurs over all educational levels and both sexes, and whether these changes are due to increasing proportions of individuals with higher education.

METHODS

Analyses are based on the German samples of the Survey on Health, Ageing and Retirement in Europe (waves 2004 and 2013).

RESULTS

Achievement levels increased over time and in all age groups. Improvements over educational levels occurred in parallel, differences between educational levels in the earlier survey were later reproduced at higher levels. Increasing proportions of individuals with higher education did not explain improvements of cognitive ability. No sex differences emerged.

CONCLUSION

Improved cognitive abilities could not be explained by upward shifts of educational levels. Improvements in higher age groups may foster improved health status and prolonged self-determined life in the older population.

A Half Century of Progress in US Student Achievement: Agency and Flynn Effects, Ethnic and SES Differences

Policymakers, conceptualized here as principals, disagree as to whether US student performance has changed over the past half century. To inform conversations, agents administered seven million psychometrically linked tests in math (m) and reading (rd) in 160 survey waves to national probability samples of cohorts born between 1954 and 2007. Estimated change in standard deviations (sd) per decade varies by agent (m: –0.10sd to 0.27sd, rd: –0.02sd to 0.12sd). Consistent with Flynn effects, median trends show larger gains in m (0.19sd) than in rd (0.04sd), though rates of progress for cohorts born since 1990 have increased in rd but slowed in m. Greater progress is shown by students tested at younger ages (m: 0.31sd, rd: 0.08sd) than when tested in middle years of schooling (m: 0.17sd, rd: 0.03sd) or toward the end of schooling (m: 0.06sd, rd: 0.02sd). Young white students progress more slowly (m: 0.28sd, rd: 0.09sd) than Asian (m: 46sd, rd: 0.28sd), black (m: 0.36sd, rd: 0.19sd), and Hispanic (m: 0.29sd, rd: 0.13sd) students. These ethnic differences generally attenuate as students age. Young students in the bottom quartile of the SES distribution show greater progress than those in the top quartile (difference in m: 0.08sd, in rd: 0.15sd), but the reverse is true for older students. Moderators likely include not only changes in families and schools but also improvements in nutrition, health care, and protection from contagious diseases and environmental risks. International data suggest that subject and age differentials may be due to moderators more general than just the United States.

Differences in Cognitive Functioning in Two Birth Cohorts Born 20 Years Apart: Data from the Interdisciplinary Longitudinal Study of Ageing

We compared neuropsychological functioning and prevalence of mild cognitive impairment (MCI) in two birth cohorts born 20 years apart when participants had reached the same age, i.e., the mid-60s. The study followed up 500 volunteers born 1930–1932 (C30) and 502 born 1950–1952 (C50). Participants underwent medical, neuropsychological, and psychiatric examinations in 1993–1996 (T1), 1997–2000 (T2), 2005–2008 (T3), and 2014–2016 (T4), including assessment of abstract thinking, memory performance, verbal fluency, visuo-spatial thinking, psychomotor speed, and attention. Healthy participants from C30 at T2 (n = 298) and from C50 at T4 (n = 205) were compared using multivariate ANCOVAs. Groups slightly differed with respect to age (C50: 63.86 ± 1.14 vs. C30: 66.80 ± 0.91; p < 0.05) and years of education (13.28 ± 2.89 vs. 14.56 ± 2.45). After correcting for age, C50 significantly outperformed C30 in all domains except concentration and verbal fluency. After additionally adjusting for education, C50 significantly outperformed C30 in declarative memory performances and abstract thinking only. Prevalence rates of MCI were 25.2% in C30 and 9.6% in C50 (p < 0.001). Our findings confirm the association between better educational attainment and enhanced cognitive performance in “younger” old individuals. While this association corresponds to the Flynn effect, various life course influences may have also contributed to better performance, including improvements in healthcare provision, medication, and lifestyle factors. Their overall effects may foster cognitive reserve and thus translate into the decline in MCI prevalence reported here.

Less-Intelligent and Unaware? Accuracy and Dunning–Kruger Effects for Self-Estimates of Different Aspects of Intelligence

People’s perceptions of their intelligence correlate only moderately with objective intelligence measures. On average, people overestimate themselves. According to the popular Dunning–Kruger effect, this is particularly true for low performers: across many domains, those in the lowest quartile overestimate their abilities the most. However, recent work using improved statistical approaches found little support for a Dunning–Kruger effect in general intelligence. We investigated accuracy and Dunning–Kruger effects for self-estimates of general, verbal, numerical, and spatial intelligence—domains that differed in how well they can be judged in the past. A total of 281 participants completed self-estimates and intelligence measures online. Self-estimates showed mostly moderate correlational accuracy that was slightly higher for numerical intelligence and lower for verbal intelligence. Across domains, participants rated their intelligence as above average. However, as their intelligence was indeed high, this was not an overestimation. While standard analyses indicated Dunning–Kruger effects in general, verbal, and spatial intelligence, improved statistical methods only yielded some support for one in verbal intelligence: people with lower verbal intelligence tended to have less self-knowledge about it. The generalizability of these findings is limited to young, highly educated populations. Nevertheless, our results contribute to a growing literature questioning the generality of the Dunning–Kruger effect.

Genetically informed, multilevel analysis of the Flynn Effect across four decades and three WISC versions

This study investigated the systematic rise in cognitive ability scores over generations, known as the Flynn Effect, across middle childhood and early adolescence (7-15 years; 291 monozygotic pairs, 298 dizygotic pairs; 89% White). Leveraging the unique structure of the Louisville Twin Study (longitudinal data collected continuously from 1957 to 1999 using the Wechsler Intelligence Scale for Children [WISC], WISC-R, and WISC-III ed.), multilevel analyses revealed between-subjects Flynn Effects-as both decrease in mean scores upon test re-standardization and increase in mean scores across cohorts-as well as within-child Flynn Effects on cognitive growth across age. Overall gains equaled approximately three IQ points per decade. Novel genetically informed analyses suggested that individual sensitivity to the Flynn Effect was moderated by an interplay of genetic and environmental factors.

Decreases in Brain Size and Encephalization in Anatomically Modern Humans

Growth in human brain size and encephalization is well documented throughout much of prehistory and believed to be responsible for increasing cognitive faculties. Over the past 50,000 years, however, both body size and brain mass have decreased but little is known about the scaling relationship between the two. Here, changes to the human brain are examined using matched body remains to determine encephalization levels across an evolutionary timespan. The results find decreases to encephalization levels in modern humans as compared to earlier Holocene H. sapiens and Late Pleistocene anatomically modern Homo. When controlled for lean body mass, encephalization changes are isometric, suggesting that much of the declines in encephalization are driven by recent increases in obesity. A meta-review of genome-wide association studies finds some evidence for selective pressures acting on human cognitive ability, which may be an evolutionary consequence of the more than 5% loss in brain mass over the past 50,000 years.

The secular trend of intelligence test scores: The Danish experience for young men born between 1940 and 2000

The present study investigated the Danish secular trend of intelligence test scores among young men born between 1940 and 2000, as well as the possible associations of birth cohort changes in family size, nutrition, education, and intelligence test score variability with the increasing secular trend. The study population included all men born from 1940 to 2000 who appeared before a draft board before 2020 (N = 1,556,770). At the mandatory draft board examination, the approximately 19-year-old men underwent a medical examination and an intelligence test. In the statistical analyses, the IQ mean and standard deviation (SD) were estimated separately for each of the included annual birth cohorts based on information from birth cohorts with available total intelligence test scores for all tested individuals (i.e. 1940-1958 and 1987-2000; the mean and SD were interpolated for the intermediate birth cohorts). Moreover, the possible associations with birth cohort changes in family size, height as a proxy for nutritional status, education, and IQ variability were investigated among those birth cohorts for whom a secular increase in intelligence test scores was found. The results showed that the estimated mean IQ score increased from a baseline set to 100 (SD: 15) among individuals born in 1940 to 108.9 (SD: 12.2) among individuals born in 1980, since when it has decreased. Focusing on the birth cohorts of 1940-1980, for whom a secular increase in intelligence test scores was found, birth cohort changes in family size, height, and education explained large proportions of the birth cohort variance in mean intelligence test scores, suggesting that these factors may be important contributors to the observed Flynn effect in Denmark.

Home Improvement: Evaluating Secular Changes in NLSY HOME-Cognitive Stimulation and Emotional Support Scores

This study evaluated changes over time in the quality of children's home environment, using the Home Observation Measurement of the Environment (HOME). Longitudinal increases in HOME scores were predicted by both theory and past empirical results. Analysis of the National Longitudinal Survey of Youth Children data (N = 5715, aged 0-14) suggested that HOME scores have been increasing, and that the increase is a family-level phenomenon. The data were a sample of children born to mothers who were approximately representative of the United States in 1979. An increase in HOME scores occurred primarily for the three age categories younger than ten. Effect sizes were of approximately the same magnitude as the Flynn effect for intelligence. These results have implications for policy and future research regarding the home environment.

The plasticity of late-onset dementia: A nationwide cohort study in Denmark

INTRODUCTION

The determinants of the secular decline in the incidence of dementia are not clear. The aim of this study was to investigate the influences of four factors-education, wealth, cerebrovascular health, and general health-on the secular decline.

METHODS

A cohort study was conducted of all individuals aged ≥65 years in Denmark from 2005 through 2018 (N = 1,757,168). Annual incidence rates of dementia and population attributable risks of the four factors were calculated and birth cohort trends were examined.

RESULTS

The incidence of dementia declined by 22.5% in men and 34.2% in women from 2005 through 2018. Population attributable risks of lower education, lower wealth, and stroke likewise declined. Independent of these improvements, the incidence of dementia fell across successive birth cohorts.

DISCUSSION

Most of the observed plasticity in late-onset dementia is associated with a risk decline across successive birth cohorts that is independent of improvements in traditional risk factors.

Cohort and Period Effects as Explanations for Declining Dementia Trends and Cognitive Aging

Studies have reported that the age-adjusted incidence of cognitive impairment and dementia may have decreased over the past two decades. Aging is the predominant risk factor for Alzheimer's disease and related dementias and for neurocognitive decline. However, aging cannot explain changes in overall age-adjusted incidence of dementia. The objective of this position paper was to describe the potential for cohort and period effects in cognitive decline and incidence of dementia. Cohort effects have long been reported in demographic literature, but starting in the early 1980s, researchers began reporting cohort trends in cognitive function. At the same time, period effects have emerged in economic factors and stressors in early and midlife that may result in reduced cognitive dysfunction. Recognizing that aging individuals today were once children and adolescents, and that research has clearly noted that childhood cognitive performance is a primary determinant of old-age cognitive performance, this is the first study that proposes the need to connect known cohort effects in childhood cognition with differences in late-life functioning.

Increasingly capable at the ripe old age? Cognitive abilities from 2004 to 2013 in Germany, Spain, and Sweden

Background

Life expectancy is increasing in most high-income countries, but gains in life years are maximized if spent in good health and if cognitive abilities are maintained until old age. Age-related decline of cognitive abilities does nevertheless occur, but the pace of decline is decisive. This was the starting point for our study that aims to examine cohort effects of cognitive aging in women and men in Germany, Spain and Sweden by analyzing changes from 2004 to 2013 by estimating cohort effects within age groups starting from the age of 50 years.

Methods

A cohort study was conducted that was based on data of the surveys 2004 (N = 6,081) and 2013 (N = 8,650) from the Survey of Health, Ageing and Retirement in Europe (SHARE). The analyses were based on data of female and male respondents aged 50 years and older. Age-specific means of verbal fluency and delayed recall from the German, Spanish and Swedish samples were the cognitive domains considered in the study.

Results

In both domains of cognitive ability the achievements in the later surveys were higher than in the earlier ones. This was found in all countries, abut achievement levels increased markedly in the German and the Spanish samples, while the scores of the Swedish samples were not significantly different.

While the highest scores were found for Sweden, Germany ranked in the middle and the lowest scores were found in the Spanish samples. Over time, the scores of the German samples approached those of Sweden.

Conclusions

From the first to the second survey, improvements of older adults’ cognitive abilities were found for all countries considered. This may indicate improvements of the underlying educational systems, but also increasingly stimulating general living conditions.

Changes in the Intelligence Levels and Structure in Russia: An ANOVA Method Based on Discretization and Grouping of Factors

In the present paper, we investigate how the general intelligence quotient (IQ) and its subtests changed for students from Russian University from 1991 to 2013. This study of the effect of such factors as gender, department, and year on the IQ response is carried out using the ANOVA model. Given the unevenness of the initial sample by years and departments, and consequently, heterogeneity of variances when divided by the original natural categories, we decided to aggregate the values of explanatory variables to build an adequate model. The paper proposes and investigates an algorithm for joint discretization and grouping, which uses the procedure of partial screening of solutions. It is an intermediate option between the greedy algorithm and exhaustive search. As a goodness function (an optimality criterion), we investigate 26 intermediate options between the AIC and BIC criteria. The BIC turned out to be the most informative and the most acceptable criterion for interpretation, which penalizes the complexity of the model, due to some decrease in accuracy. The resulting partition of the explanatory variables values into categories is used to interpret the modeling results and to arrive at the final conclusions of the data analysis. As a result, it is revealed that the observed features of the IQ dynamics are caused by changes in the education system and the socio-economic status of the family that occurred in Russia during the period of restructuring the society and intensive development of information technologies.

Cultural Evolution of Genetic Heritability

Behavioral genetics and cultural evolution have both revolutionized our understanding of human behavior-largely independent of each other. Here we reconcile these two fields under a dual inheritance framework, offering a more nuanced understanding of the interaction between genes and culture. Going beyond typical analyses of gene-environment interactions, we describe the cultural dynamics that shape these interactions by shaping the environment and population structure. A cultural evolutionary approach can explain, for example, how factors such as rates of innovation and diffusion, density of cultural sub-groups, and tolerance for behavioral diversity impact heritability estimates, thus yielding predictions for different social contexts. Moreover, when cumulative culture functionally overlaps with genes, genetic effects become masked, unmasked, or even reversed, and the causal effects of an identified gene become confounded with features of the cultural environment. The manner of confounding is specific to a particular society at a particular time, but a WEIRD (Western, educated, industrialized, rich, democratic) sampling problem obscures this boundedness. Cultural evolutionary dynamics are typically missing from models of gene-to-phenotype causality, hindering generalizability of genetic effects across societies and across time. We lay out a reconciled framework and use it to predict the ways in which heritability should differ between societies, between socioeconomic levels and other groupings within some societies but not others, and over the life course. An integrated cultural evolutionary behavioral genetic approach cuts through the nature-nurture debate and helps resolve controversies in topics such as IQ.

Mitochondrial Functioning and the Relations among Health, Cognition, and Aging: Where Cell Biology Meets Cognitive Science

Cognitive scientists have determined that there is a set of mechanisms common to all sensory, perceptual, and cognitive abilities and correlated with age- and disease-related declines in cognition. These mechanisms also contribute to the development and functional coherence of the large-scale brain networks that support complex forms of cognition. At the same time, these brain and cognitive patterns are correlated with myriad health outcomes, indicating that at least some of the underlying mechanisms are common to all biological systems. Mitochondrial functions, including cellular energy production and control of oxidative stress, among others, are well situated to explain the relations among the brain, cognition, and health. Here, I provide an overview of the relations among cognitive abilities, associated brain networks, and the importance of mitochondrial energy production for their functioning. These are then linked to the relations between cognition, health, and aging. The discussion closes with implications for better integrating research in cognitive science and cell biology in the context of developing more sensitive measures of age- and disease-related declines in cognition.

Grandchild's IQ is associated with grandparental environments prior to the birth of the parents

Background. Despite convincing animal experiments demonstrating the potential for environmental exposures in one generation to have demonstrable effects generations later, there have been few relevant human studies. Those that have been undertaken have demonstrated associations, for example, between exposures such as nutrition and cigarette smoking in the grandparental generation and outcomes in grandchildren. We hypothesised that such transgenerational associations might be associated with the IQ of the grandchild, and that it would be likely that there would be differences in results between the sexes of the grandparents, parents, and children. Method. We used three-generational data from the Avon Longitudinal Study of Parents and Children (ALSPAC).  We incorporated environmental factors concerning grandparents (F0) and focussed on three exposures that we hypothesised may have independent transgenerational associations with the IQ of the grandchildren (F2): (i) UK Gross Domestic Product (GDP) at grandparental birth year; (ii) whether grandfather smoked; and (iii) whether the grandmother smoked in the relevant pregnancy. Potential confounders were ages of grandparents when the relevant parent was born, ethnic background, education level and social class of each grandparent. Results. After adjustment, all three target exposures had specific associations with measures of IQ in the grandchild. Paternal grandfather smoking was associated with reduced total IQ at 15 years; maternal grandfather smoking with reduced performance IQ at 8 years and reduced total IQ at 15.  Paternal grandmother smoking in pregnancy was associated with reduced performance IQ at 8, especially in grandsons. GDP at grandparents' birth produced independent associations of reduced IQ with higher GDP; this was particularly true of paternal grandmothers. Conclusions. These results are complex and need to be tested in other datasets. They highlight the need to consider possible transgenerational associations in studying developmental variation in populations.