Increasing IQ Test Scores and Decreasing g: The Flynn Effect and Decreasing Positive Manifold Strengths in Austria (2005-2018)

After almost a century of global generational IQ test score gains, the Flynn effect has, in the past decades, been observed to show stagnation and reversals in several countries. Tentative evidence from academic achievement data has suggested that these trajectory changes may be rooted in a decreasing strength of the positive manifold of intelligence due to increasing ability differentiation and specialization in the general population. Here, we provide direct evidence for generational IQ test score and positive manifold strength changes based on IQ test standardization data from 1392 Austrian residents between 2005 and 2018. Our analyses revealed positive Flynn effects across all domains of the IQ test (Cohen's d from 0.21 to 0.91) but a trend toward decreasing strength in the positive manifold of intelligence (R2 from .908 to .892), though these changes were not statistically significant. Our results are consistent with the idea that increasingly inconsistent Flynn effect trajectories may be attributed to increasing ability differentiation and specialization in the general population over time.

Assessment of cognitive functions and adaptive behavior in children with end-stage renal disease on regular hemodialysis

Chronic kidney disease (CKD) is defined by the Kidney Disease and Outcome Quality Initiative as a child who has kidney damage lasting for at least three months with or without decreased glomerular filtration rate. Hemodialysis (HD) means removal of waste products and extra fluid directly from the blood when the kidneys do not work properly. Studies aimed at investigating neurocognitive impairment in children with CKD have identified a wide range of delays in cognitive development. The aim of this study was to assess the cognitive functions and adaptive behavior in children with end-stage renal disease (ESRD) on regular HD. This case-controlled study was conducted on 30 children suffering from ESRD who were on treatment at the Pediatric Nephrology Unit of Tanta University Hospital. Thirty apparently healthy children served as a control group, in the period from January 2017 to January 2018. All children were subjected to full history taking, careful physical and neurological examination, specific investigations including assessment of intelligence quotient (IQ) using Stanford Binet test 5^th edition; assessment of adaptive behavior, assessment of executive functions by using Wisconsin Card Sorting Test; and continuous performance test. This study showed that mean values of IQ and the Vineland test were significantly lower among patients than controls. The study suggests that children with ESRD had lower IQ, adaptive behavior and executive functions than healthy control children.

Neurocognitive and Educational Outcomes in Children and Adolescents with CKD: A Systematic Review and Meta-Analysis

BACKGROUND AND OBJECTIVES

Poor cognition can affect educational attainment, but the extent of neurocognitive impairment in children with CKD is not well understood. This systematic review assessed global and domain-specific cognition and academic skills in children with CKD and whether these outcomes varied with CKD stage.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Electronic databases were searched for observational studies of children with CKD ages 21 years old or younger that assessed neurocognitive or educational outcomes. Risk of bias was assessed using a modified Newcastle-Ottawa scale. We used random effects models and expressed the estimates as mean differences with 95% confidence intervals stratified by CKD stage.

RESULTS

Thirty-four studies (25 cross-sectional, n=2095; nine cohort, n=991) were included. The overall risk of bias was high because of selection and measurement biases. The global cognition (full-scale intelligence quotient) of children with CKD was classified as low average. Compared with the general population, the mean differences (95% confidence intervals) in full-scale intelligence quotient were -10.5 (95% confidence interval, -13.2 to -7.72; all CKD stages, n=758), -9.39 (95% confidence interval, -12.6 to -6.18; mild to moderate stage CKD, n=582), -16.2 (95% confidence interval, -33.2 to 0.86; dialysis, n=23), and -11.2 (95% confidence interval, -17.8 to -4.50; transplant, n=153). Direct comparisons showed that children with mild to moderate stage CKD and kidney transplants scored 11.2 (95% confidence interval, 2.98 to 19.4) and 10.1 (95% confidence interval, -1.81 to 22.0) full-scale intelligence quotient points higher than children on dialysis. Children with CKD also had lower scores than the general population in executive function and memory (verbal and visual) domains. Compared with children without CKD, the mean differences in academic skills (n=518) ranged from -15.7 to -1.22 for mathematics, from -9.04 to -0.17 for reading, and from -14.2 to 2.53 for spelling.

CONCLUSIONS

Children with CKD may have low-average cognition compared with the general population, with mild deficits observed across academic skills, executive function, and visual and verbal memory. Limited evidence suggests that children on dialysis may be at greatest risk compared with children with mild to moderate stage CKD and transplant recipients.

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.

Flaws in Flynn Effect Research With the Wechsler Scales

Many Flynn effect (FE) studies compare scores across different editions of Wechsler’s IQ tests. When construct changes are introduced by the test developers in the new edition, however, the presumed generational effects are difficult to untangle from changes due to test content. To remove this confound, we use the same edition of Wechsler Intelligence Scale for Children–Fourth Edition (WISC-IV) across an 11-year period. Whereas previous research has reported the FE to be less than half the theoretical rate when comparing WISC-IV with Wechsler Intelligence Scale for Children–Fifth Edition (WISC-V), we find the rate of gain to be nearly identical to Flynn’s prediction when comparing only WISC-IV scores over the same time period. The FE is shown to vary significantly across the domains of cognitive ability, and thus changes to the construct coverage of the WISC-V Full Scale IQ (FSIQ) composite between editions significantly affect FE findings. Implications for future FE research are discussed.

When does cognitive functioning peak? The asynchronous rise and fall of different cognitive abilities across the life span

Understanding how and when cognitive change occurs over the life span is a prerequisite for understanding normal and abnormal development and aging. Most studies of cognitive change are constrained, however, in their ability to detect subtle, but theoretically informative life-span changes, as they rely on either comparing broad age groups or sparse sampling across the age range. Here, we present convergent evidence from 48,537 online participants and a comprehensive analysis of normative data from standardized IQ and memory tests. Our results reveal considerable heterogeneity in when cognitive abilities peak: Some abilities peak and begin to decline around high school graduation; some abilities plateau in early adulthood, beginning to decline in subjects' 30s; and still others do not peak until subjects reach their 40s or later. These findings motivate a nuanced theory of maturation and age-related decline, in which multiple, dissociable factors differentially affect different domains of cognition.

Cognitive Tests in Early Childhood

Cognitive assessment of young children contributes to high-stakes decisions because results are often used to determine eligibility for early intervention and special education. Previous reviews of cognitive measures for young children highlighted concerns regarding adequacy of standardization samples, steep item gradients, and insufficient floors for young children functioning at lower levels. The present report extends previous reviews by including measures recently published or revised, nonverbal cognitive assessment tools, and issues specific to assessing bilingual or non-English-speaking children. Sixteen tests were reviewed, including all available measures of cognitive functioning for 2- to 4-year-old children normed in the United States. Test characteristics evaluated included (a) representativeness and recency of standardization data, (b) item bias analysis, (c) psychometric characteristics, and (d) appropriateness for assessing young children with developmental delays and non-English-speaking children. Implications are discussed for clinicians, researchers, and test developers.

Changes in Word Usage Frequency May Hamper Intergenerational Comparisons of Vocabulary Skills

Research on secular trends in mean intelligence test scores shows smaller gains in vocabulary skills than in nonverbal reasoning. One possible explanation is that vocabulary test items become outdated faster compared to nonverbal tasks. The history of the usage frequency of the words on five popular vocabulary tests, the GSS Wordsum, Wechsler Adult Intelligence Scale (WAIS), Wechsler Adult Intelligence Scale–Revised (WAIS-R), Wechsler Intelligence Scale for Children (WISC), and Wechsler Intelligence Scale for Children–Revised (WISC-R) IQ tests, was analyzed by means of the Google ngram viewer. Usage frequency had a 0.38 to 0.73 correlation with item difficulty. In the period between test standardizations, the median change in usage frequency was −17% for WISC words, −8% for Wordsum, −5% for WISC-R, −4% for WAIS, and 0% for WAIS-R words. The correlation between median change in usage frequency and gain in vocabulary score was 0.33. Further studies with a larger set of vocabulary tests are needed to analyze in more detail the magnitude of the effect of changing word usage frequencies.

The Increase in Colored Progressive Matrices Test Performance in Individuals With Down Syndrome: A Qualitative and Quantitative Review

It is well known that a normal population improves its IQ test scores by about 3 points per decade. This is called the Flynn effect and has been explained in different and sometimes contrasting ways. Few and ambiguous data are available on any Flynn effect in individuals with an atypical development, such as those with intellectual disabilities: some studies report evidence of the Flynn effect, whereas others do not. The main objective of the present study was to analyze the performance of individuals with Down syndrome (DS) compared with a sample of typically developing (TD) children in the Colored Progressive Matrices (CPM) test, which measures abstract reasoning and is commonly used to estimate IQ, to see whether a Flynn effect is present. Our results suggest that the Flynn effect in the DS population depends on the individual’s age.

Standard of practice and Flynn Effect testimony in death penalty cases

The Flynn Effect is a well-established psychometric fact documenting substantial increases in measured intelligence test performance over time. Flynn's (1984) review of the literature established that Americans gain approximately 0.3 points per year or 3 points per decade in measured intelligence. The accurate assessment and interpretation of intellectual functioning becomes critical in death penalty cases that seek to determine whether an individual meets the criteria for intellectual disability and thereby is ineligible for execution under Atkins v. Virginia (2002) . We reviewed the literature on the Flynn Effect and demonstrated how failure to adjust intelligence test scores based on this phenomenon invalidates test scores and may be in violation of the Standards for Educational and Psychological Testing as well as the "Ethical Principles for Psychologists and Code of Conduct." Application of the Flynn Effect and score adjustments for obsolete norms clearly is supported by science and should be implemented by practicing psychologists.

Pervasiveness of the IQ rise: a cross-temporal meta-analysis

BACKGROUND

Generational IQ gains in the general population (termed the Flynn effect) show an erratic pattern across different nations as well as across different domains of intelligence (fluid vs crystallized). Gains of fluid intelligence in different countries have been subject to extensive research, but less attention was directed towards gains of crystallized intelligence, probably due to evidence from the Anglo-American sphere suggesting only slight gains on this measure. In the present study, development of crystallized intelligence in the German speaking general population is assessed.

METHODOLOGY/PRINCIPAL FINDINGS

To investigate whether IQ gains for crystallized intelligence are in progress in German-speaking countries, two independent meta-analyses were performed. By means of a cited reference search in ISI Web of Science, all studies citing test manuals and review articles of two widely-used salient measures of crystallized intelligence were obtained. Additionally, the electronic database for German academic theses was searched to identify unpublished studies employing these tests. All studies reporting participants mean IQ or raw scores of at least one of the two measures were included in the present analyses, yielding over 500 studies (>1,000 samples; >45,000 individuals). We found a significant positive association between years of test performance and intelligence (1971-2007) amounting to about 3.5 IQ points per decade.

CONCLUSIONS/SIGNIFICANCE

This study clearly demonstrates that crystallized IQ gains are substantial and of comparable strength as Flynn effects typically observed for measures of fluid intelligence in Central Europe. Since mean IQ was assessed in a large number of small, non-representative samples, our evidence suggests a remarkable robustness of these gains. Moreover, in both meta-analyses strength of gains was virtually identical. On the whole, results of the present study demonstrate a pervasive and generalizing Flynn effect in German-speaking countries.

IQ Scores Should Be Corrected for the Flynn Effect in High-Stakes Decisions

IQ test scores should be corrected for high stakes decisions that employ these assessments, including capital offense cases. If scores are not corrected, then diagnostic standards must change with each generation. Arguments against corrections, based on standards of practice, information present and absent in test manuals, and related issues, ignore expert consensus about the assessment of intellectual disabilities and the acceptance of the Flynn effect in the field. Most psychometric concerns about correction are based on validity studies with small subgroups and do not reflect sufficient effort to estimate the precision of the Flynn estimate. We computed a confidence interval for the Wechsler PIQ across four validity studies that shows a SEM of about 1 around a mean of about 3 points per decade. A meta-analytic weighted mean of the 14 studies in Flynn (2009) is 2.80 (2.50, 3.09), close to Flynn’s (2009) unweighted average (2.99). More psychometric research would be helpful, but this level of precision supports the Flynn adjustment of 3 points per decade.

Considerations on the Flynn Effect

Flynn has proposed a grand integrative theory, which he calls “scientific spectacles,” to explain the phenomenon of rising IQ scores across multiple decades known as the Flynn effect (FE). In his theory, he purports that modern society has placed increasing value and emphasis on the application and education of scientific principles—which include abstract fluid reasoning—and this has mirrored larger score increases in the abstract fluid reasoning tasks included as part of most intelligence tests. He highlights huge gains in the Wechsler Similarities subtest over time as one linchpin supporting his theory that fluid reasoning is rising faster than other aspects of intelligence, but further points to large increases in Wechsler performance tasks (i.e., perceptual organization and reasoning) relative to crystallized tasks, and to the many studies of Raven’s Progressive Matrices, which is widely held to be a fairly pure measure of fluid reasoning. As with any new theory of this magnitude, Flynn’s grand proposal has invited numerous criticisms that must now be addressed—and this is as it should be in the spirit of scientific progress. Each of these issues is multilayered and has many legitimate perspectives. The present article attempts to carefully consider each issue and perspective in sequence.

Looking Through Flynn’s Rose-Colored Scientific Spectacles

In the first article of this special issue of the Journal of Psychoeducational Assessment, I critiqued Flynn’s theoretical explanation of the Flynn effect because he depended too heavily on an apparently huge generational gain on the WISC Similarities subtest; I claimed he was comparing apples with oranges because that subtest changed too much when the WISC was first revised. Four sets of esteemed researchers were invited to respond to my article and also to an article by Zhou, Zhu, and Weiss—Flynn, Sternberg, McGrew, and Ceci and Kanaya. Flynn disagrees strongly with my critique of his theory, a theory that posits striking generational shifts from concrete (utilitarian) thinking to a kind of fluid reasoning that Flynn nicknames “scientific spectacles.” In this final article of the special issue, I respond to Flynn’s claims, and also to the points made by the other invited respondents. In addition, I respond to the range of opinions expressed by the scholars who were invited to write an essay on whether or not IQs should be adjusted for the Flynn effect in capital punishment cases (Fletcher et al., Hagan et al., and Reynolds et al.). Ultimately, I disagree with Flynn’s explanation of the Flynn effect, but I agree with his position that IQs should be adjusted for the effect in death penalty cases.