Factor structure and sex differences on the Wechsler Preschool and Primary Scale of Intelligence in China, Japan and United States

Inhibiting proBDNF to mature BDNF conversion leads to ASD-like phenotypes in vivo

Autism Spectrum Disorders (ASD) comprise a range of early age-onset neurodevelopment disorders with genetic heterogeneity. Most ASD related genes are involved in synaptic function, which is regulated by mature brain-derived neurotrophic factor (mBDNF) and its precursor proBDNF in a diametrically opposite manner: proBDNF inhibits while mBDNF potentiates synapses. Here we generated a knock-in mouse line (BDNFmet/leu) in which the conversion of proBDNF to mBDNF is attenuated. Biochemical experiments revealed residual mBDNF but excessive proBDNF in the brain. Similar to other ASD mouse models, the BDNFmet/leu mice showed reduced dendritic arborization, altered spines, and impaired synaptic transmission and plasticity in the hippocampus. They also exhibited ASD-like phenotypes, including stereotypical behaviors and deficits in social interaction. Moreover, the plasma proBDNF/mBDNF ratio was significantly increased in ASD patients compared to normal children in a case-control study. Thus, deficits in proBDNF to mBDNF conversion in the brain may contribute to ASD-like behaviors, and plasma proBDNF/mBDNF ratio may be a potential biomarker for ASD.

Intelligenz‍(tests) verstehen und missverstehen

Zusammenfassung. Die vorliegende Standortbestimmung zeigt die hohe wissenschaftliche Qualität der Intelligenzforschung und von Intelligenztests. Es werden aber auch mögliche Missverständnisse und Einseitigkeiten der Ergebnisrezeption und -interpretation thematisiert. Im Einzelnen werden (1) die hohe prognostische und kriterienbezogene Validität bei gleichzeitigen Vorbehalten wie teils niedriger Akzeptanz bzw. Augenscheinvalidität, (2) die Darstellung empirischer Befunde aus der Perspektive ausgewählter Theorien sowie (3) die Bedeutung von Umwelteinflüssen und hohen Erblichkeitskoeffizienten eingehender betrachtet. Für jeden dieser Bereiche wird verdeutlicht, dass vor allem Präzision bei der Rezeption und Darstellung von Forschungsergebnissen notwendig ist, um Einseitigkeiten, Missverständnisse und Instrumentalisierungen zu vermeiden. Der vorliegende Beitrag zeigt, dass einiges, was als Problem der Intelligenzforschung und von Intelligenztests kritisiert wird, letztendlich auf die dargestellten Missverständnisse zurückzuführen ist. Vor diesem Hintergrund wird der Unterschied zwischen der qualitativ hochwertigen Intelligenzforschung und Intelligenztestung einerseits sowie den Missverständnissen und Einseitigkeiten bei der Rezeption andererseits herausgearbeitet. Weiterhin werden berechtigte Kritikpunkte an der Intelligenzforschung und an Intelligenztests sowie Forschungsdesiderata benannt.

Breakfast Consumption Habits at Age 6 and Cognitive Ability at Age 12: A Longitudinal Cohort Study

This study aimed to assess the relationship between breakfast composition and long-term regular breakfast consumption and cognitive function. Participants included 835 children from the China Jintan Cohort Study for the cross-sectional study and 511 children for the longitudinal study. Breakfast consumption was assessed at ages 6 and 12 through parental and self-administered questionnaires. Cognitive ability was measured as a composition of IQ at age 6 and 12 and academic achievement at age 12, which were assessed by the Chinese versions of the Wechsler Intelligence Scales and standardized school reports, respectively. Multivariable general linear and mixed models were used to evaluate the relationships between breakfast consumption, breakfast composition and cognitive performance. In the longitudinal analyses, 94.7% of participants consumed breakfast ≥ 4 days per week. Controlling for nine covariates, multivariate mixed models reported that compared to infrequent breakfast consumption, regular breakfast intake was associated with an increase of 5.54 points for verbal and 4.35 points for full IQ scores (p < 0.05). In our cross-sectional analyses at age 12, consuming grain/rice or meat/egg 6-7 days per week was significantly associated with higher verbal, performance, and full-scale IQs, by 3.56, 3.69, and 4.56 points, respectively (p < 0.05), compared with consuming grain/rice 0-2 days per week. Regular meat/egg consumption appeared to facilitate academic achievement (mean difference = 0.232, p = 0.043). No association was found between fruit/vegetable and dairy consumption and cognitive ability. In this 6-year longitudinal study, regular breakfast habits are associated with higher IQ. Frequent grain/rice and meat/egg consumption during breakfast may be linked with improved cognitive function in youth.

Sex Differences in Gains Among Hispanic Pre-kindergartners' Mental Rotation Skills

The current study explores change in mental rotation skills throughout the pre-kindergarten year in a Hispanic population to better understand the development of early sex differences in mental rotation. Ninety-six Hispanic children (M = 4 years 8 months) completed a mental rotation task at the beginning and end of pre-kindergarten. Results suggest Hispanic boys and girls differed in gains on mental rotation ability, with boys improving significantly more than girls during pre-kindergarten on a mental rotation task. This study highlights the significance of studying mental rotation abilities in a Hispanic population of pre-kindergarten aged children and suggests the importance of examining sex differences in mental rotation over time, rather than at one time-point, to better understand when sex differences in spatial skills develop. We discuss various factors that potentially affect the growth of spatial skills including the role of early education, spatial experiences, and spatial language input.

Neuropsychological Profile Related with Executive Function of Chinese Preschoolers with Attention-Deficit/Hyperactivity Disorder: Neuropsychological Measures and Behavior Rating Scale of Executive Function-Preschool Version

Background:

Previous studies have found that schoolchildren with attention-deficit/hyperactivity disorder (ADHD) showed difficulties in neuropsychological function. This study aimed to assess neuropsychological function in Chinese preschoolers with ADHD using broad neuropsychological measures and rating scales and to test whether the pattern and severity of neuropsychological weakness differed among ADHD presentations in preschool children.

Methods:

The 226 preschoolers (163 with ADHD and 63 controls) with the age of 4–5 years were included and assessed using the Behavior Rating Scale of Executive Function-Preschool Version (BRIEF-P) and a series of tests to investigate neuropsychological function.

Results:

Preschoolers with ADHD showed higher scores in all domains of the BRIEF-P (inhibition: 30.64 ± 5.78 vs.20.69 ± 3.86, P < 0.001; shift: 13.40 ± 3.03 vs.12.41 ± 2.79, P = 0.039; emotional control:15.10 ± 3.53 vs.12.20 ± 2.46, P < 0.001; working memory: 28.41 ± 4.99 vs.20.95 ± 4.60, P < 0.001; plan/organize: 17.04 ± 3.30 vs.13.29 ± 2.40, P < 0.001) and lower scores of Statue (23.18 ± 7.84 vs.28.27 ± 3.18, P = 0.001), Word Generation (15.22 ± 6.52 vs.19.53 ± 7.69, P = 0.025), Comprehension of Instructions (14.00 ± 4.44 vs.17.02 ± 3.39, P = 0.016), Visuomotor Precision (P < 0.050), Toy delay (P = 0.048), and Matrices tasks (P = 0.011), compared with normal control. In terms of the differences among ADHD subtypes, all ADHD presentations had higher scores in several domains of the BRIEF-P (P < 0.001), and the ADHD-combined symptoms (ADHD-C) group had the poorest ratings on inhibition and the ability to Plan/Organize. For neuropsychological measures, the results suggested that the ADHD-C group had poorer performances than the ADHD-predominantly inattentive symptoms (ADHD-I) group on Statue tasks (F = 7.34, η² = 0.12, P < 0.001). Furthermore, the ADHD-hyperactive/impulsive symptoms group had significantly poorer performances compared to the ADHD-C group in the Block Construction task (F = 4.89, η² = 0.067, P = 0.003). However, no significant group differences were found between the ADHD-I group and normal control.

Conclusion:

Based on the combined evaluation of performance-based neuropsychological tests and the BRIEF-P, preschoolers with ADHD show difficulties of neuropsychological function in many aspects.

Sex differences in the intellectual functioning of early school-aged children in rural China

Background

Gender disparities in China are concentrated in poor rural areas and among poor households. The difference in intelligence between boys and girls is less clear in rural China. The purpose of this paper was to assess sex differences in the intellectual function of early school-aged children in rural China.

Methods

One thousand seven hundred forty four early school-aged offspring of women who had participated in a prenatal supplementation trial with different combinations of micronutrients and continued to reside in two rural counties in China were followed. We measured their Full-Scale IQ (FSIQ), Verbal Comprehension Index (VCI), Working Memory Index (WMI), Perceptual Reasoning Index (PRI) and Processing Speed Index (PSI) using the Wechsler Intelligence Scale for Children (WISC-IV). Multilevel analyses were used to assess sex differences in intellectual functioning in 7-10-year-old children in rural China.

Results

Boys’ adjusted mean FSIQ score was 0.97 points higher (95 % CI: -2.22 − 0.28) than that of girls. Girls obtained higher mean WMI and PSI scores, with 1.32 points (95 % CI: 0.14 − 2.51) and 3.10 points (95 % CI: 1.82–4.38) higher adjusted means, respectively. Boys’ adjusted mean VCI and PRI scores were significantly higher than those of girls, and the mean differences were 2.44 points (95 % CI: 0.95 − 3.94) and 3.68 points (95 % CI: 2.36 − 5.01), respectively.

Conclusions

There is no evidence to suggest sex differences in the general intelligence of early school-aged children in rural China. However, a difference in general intelligence between 10-year-old boys and girls was evident. Girls and boys in rural China tended to show different specific cognitive abilities.

Cohort Profile Update: The China Jintan Child Cohort Study

The China Jintan Child Cohort study began in 2004 with 1656 pre-school participants and a research focus on studying the impact of environmental exposures, such as lead, on children's neurobehavioural outcomes. This population cohort now includes around 1000 of the original participants, who have been assessed three times over a period of 10 years. Since the original IJE cohort profile publication in 2010, participants have experienced a critical developmental transition from pre-school to school age and then adolescence. The study has also witnessed an increase in breadth and depth of data collection from the original aim of risk assessment. This cohort has added new directions to investigate the mechanisms and protective factors for the relationship between early health factors and child physical and mental health outcomes, with an emphasis on neurobehavioural consequences. The study now encompasses 11 domains, composed of repeated measures of the original variables and new domains of biomarkers, sleep, psychophysiology, neurocognition, personality, peer relationship, mindfulness and family dynamics. Depth of evaluation has increased from parent/teacher report to self/peer report and intergenerational family report. Consequently, the cohort has additional directions to include: (i) classmates of the original cohort participants for peer relationship assessment; and (ii) parental and grandparental measures to assess personality and dynamics within families. We welcome interest in our study and ask investigators to contact the corresponding author for additional information on data acquisition.

The Long Term Impact of Micronutrient Supplementation during Infancy on Cognition and Executive Function Performance in Pre-School Children

Brain growth and development are critically dependent on several micronutrients. During early development cellular activity may be sensitive to micronutrient deficiencies, however the evidence from human studies is equivocal. The objective of this study was to examine the long-term cognitive and social-emotional effects of multiple micronutrient supplementation compared with iron supplementation alone, administered during infancy. This study was a follow-up to an initial randomized, double-blind controlled trial (RCT) in 2010 in which 902 infants, aged 6–17 months, from Lima, Peru, were given daily supplements of either iron (Fe) or multiple micronutrients (MMN) including zinc (451 in each group). The supplementation period for both groups was six months. In 2012, a subsample of 184 children from the original cohort (now aged 36–48 months) was randomly selected to participate in a follow-up trial and was assessed for intelligence, working memory, inhibition, and executive function. The tests showed no significant differences between the supplementation groups though there were some gender differences, with girls displaying higher scores than boys across both groups on the Wechsler Preschool and Primary Scale of Intelligence (WPPSI) Verbal IQ sentences subtest, the Day-Night cognitive test and on the Brief Infant-Toddler Social Emotional Assessment (BITSEA) social competency, and boys scoring higher than girls in problem behaviour. The results indicate that MMN supplementation had no long term additional effects on cognitive function compared with iron supplementation alone. The timing of supplement administration for maximum impact on a child’s cognitive development requires further investigation.

Comparing Intelligence Quotient (IQ)among 3 to 7-year-old strabismic and nonstrabismic children in an Iranian population

This study was designed to compare the Intelligence Quotient (IQ) among 3 to 7-year-old strabismic and nonstrabismic children in an Iranian population.

In this cross-sectional study, 108 preschool children with equal numbers of strabismic/non-strabismic disorder (age 3–7 years) were randomly selected from exceptional strabismus clinics of Ahvaz and were evaluated with the preschool and primary scale of intelligence versions of Wechsler (WPPSI).

In the current study, 108 children were evaluated. In strabismic patients the mean performance, verbal and total IQ were 89.46±19.79, 89.57±21.57 and 91.54±22.08 respectively. These mean scores in normal children were 91.89±47.53, 87.56±15.6 and 89.96±17.62consecuently. The results showed that these three different IQ subscales were not significantly different among 3 to 7 years old strabismic and nonstrabismic children ((P>0.05 for all comparisons). There was no significant difference in IQ between two sexes (P>0.05) while Persian tribe children had greater IQ score compared to other tribes (P<0.05). Also, higher paternal educational status of children related to higher IQ score. IQ score was better in combined deviations and was higher in exotropes than esotropes; however, these differences were not statistically significant (P>0.05).

In this evaluation, we did not found a significant negative interference of strabismus on IQ score of preschool children. It can be concluded that paternal educational level and tribe have a significant effect on intelligent quotient, while this is not the case on sex and ocular deviation.

Chinese sex differences in intelligence: Some new evidence

Sex differences on the WISC-R in Chinese children were examined in a sample of 788 aged 12 years. Boys obtained a higher mean full scale IQ than girls of 3.75 IQ points, a higher performance IQ of 4.20 IQ points, and a higher verbal IQ of 2.40 IQ points. Boys obtained significantly higher means on the information, picture arrangement, picture completion, block design, and object assembly subtests, while girls obtained a significantly higher mean on coding. The results were in general similar to the sex differences in the United States standardisation sample of the WISC-R. Boys showed greater variability than girls.

Blood lead concentrations and children's behavioral and emotional problems: a cohort study

IMPORTANCE

The association between lead exposure and children's IQ has been well studied, but few studies have examined the effects of blood lead concentrations on children's behavior.

OBJECTIVE

To evaluate the association between blood lead concentrations and behavioral problems in a community sample of Chinese preschool children with a mean blood lead concentration of less than 10 µg/dL.

DESIGN, SETTING, AND PARTICIPANTS

A prospective cohort study was conducted at 4 preschools in Jintan, Jiangsu province of China. Participants included 1341 children aged 3 to 5 years.

EXPOSURES

Lead.

MAIN OUTCOMES AND MEASURES

Blood lead concentrations were measured in children aged 3 to 5 years. Behavioral problems were assessed using Chinese versions of the Child Behavior Checklist and Caregiver-Teacher Report Form when children were aged 6 years.

RESULTS

The mean (SD) blood lead concentration was 6.4 (2.6) µg/dL, with the 75th and 90th percentiles being 7.5 and 9.4 µg/dL, respectively. General linear modeling showed significant associations between blood lead concentrations and increased scores for teacher-reported behavioral problems. A 1-µg/dL increase in the blood lead concentration resulted in a 0.322 (95% CI, 0.058 to 0.587), 0.253 (95% CI, 0.016 to 0.500), and 0.303 (95% CI, 0.046 to 0.560) increase of teacher-reported behavior scores on emotional reactivity, anxiety problems, and pervasive developmental problems, respectively (P < .05), with adjustment for parental and child variables. Spline modeling showed that mean teacher-reported behavior scores increased with blood lead concentrations, particularly for older girls.

CONCLUSIONS AND RELEVANCE

Blood lead concentrations, even at a mean concentration of 6.4 µg/dL, were associated with increased risk of behavioral problems in Chinese preschool children, including internalizing and pervasive developmental problems. This association showed different patterns depending on age and sex. As such, continued monitoring of blood lead concentrations, as well as clinical assessments of mental behavior during regular pediatric visits, may be warranted.

Reliability and validity of the new Tanaka B Intelligence Scale scores: a group intelligence test

Objective

The present study evaluated the reliability and concurrent validity of the new Tanaka B Intelligence Scale, which is an intelligence test that can be administered on groups within a short period of time.

Methods

The new Tanaka B Intelligence Scale and Wechsler Intelligence Scale for Children-Third Edition were administered to 81 subjects (mean age ± SD 15.2±0.7 years) residing in a juvenile detention home; reliability was assessed using Cronbach’s alpha coefficient, and concurrent validity was assessed using the one-way analysis of variance intraclass correlation coefficient. Moreover, receiver operating characteristic analysis for screening for individuals who have a deficit in intellectual function (an FIQ<70) was performed. In addition, stratum-specific likelihood ratios for detection of intellectual disability were calculated.

Results

The Cronbach’s alpha for the new Tanaka B Intelligence Scale IQ (BIQ) was 0.86, and the intraclass correlation coefficient with FIQ was 0.83. Receiver operating characteristic analysis demonstrated an area under the curve of 0.89 (95% CI: 0.85–0.96). In addition, the stratum-specific likelihood ratio for the BIQ≤65 stratum was 13.8 (95% CI: 3.9–48.9), and the stratum-specific likelihood ratio for the BIQ≥76 stratum was 0.1 (95% CI: 0.03–0.4). Thus, intellectual disability could be ruled out or determined.

Conclusion

The present results demonstrated that the new Tanaka B Intelligence Scale score had high reliability and concurrent validity with the Wechsler Intelligence Scale for Children-Third Edition score. Moreover, the post-test probability for the BIQ could be calculated when screening for individuals who have a deficit in intellectual function. The new Tanaka B Intelligence Test is convenient and can be administered within a variety of settings. This enables evaluation of intellectual development even in settings where performing intelligence tests have previously been difficult.

An Increase of Intelligence in China 1986-2012

The Flynn effect has been widely researched in Western and European nations, while it has been comparatively understudied in Asian countries. This study examines possible Flynn effects in China from 1985-86 and to 2011-12. Results are reported for an IQ increase among 12 year olds on the Full Scale IQ WISC-R (Wechsler Intelligence Scale for Children- Revised) of 6.19 IQ points, a gain on the Performance IQ of 6.55 IQ points, and a gain on the Verbal IQ of 1.91 IQ points.

Impact of low blood lead concentrations on IQ and school performance in Chinese children

Objectives

Examine the relationships between blood lead concentrations and children's intelligence quotient (IQ) and school performance.

Participants and Methods

Participants were 1341 children (738 boys and 603 girls) from Jintan, China. Blood lead concentrations were measured when children were 3–5 years old. IQ was assessed using the Chinese version and norms of the Wechsler Preschool and Primary Scale of Intelligence – Revised when children were 6 years old. School performance was assessed by standardized city tests on 3 major subjects (Chinese, Math, and English [as a foreign language]) when children were age 8–10 years.

Results

Mean blood lead concentration was 6.43 µg/dL (SD = 2.64). For blood lead concentrations, 7.8% of children (n = 105) had ≥10.0 µg/dL, 13.8% (n = 185) had 8.0 to <10.0 µg/dL, and 78.4% (n = 1051) had <8.0 µg/dL. Compared to children with blood lead concentrations <8 µg/dL, those with blood lead concentrations ≥8 µg/dL scored 2–3 points lower in IQ and 5–6 points lower in school tests. There were no significant differences in IQ or school tests between children with blood lead concentrations groups 8–10 and ≥10 µg/dL. After adjustment for child and family characteristics and IQ, blood lead concentrations ≥10 µg/dL vs <8 µg/dL at ages 3–5 years was associated with reduced scores on school tests at age 8–10 years (Chinese, β = −3.54, 95%CI = −6.46, −0.63; Math, β = −4.63, 95%CI = −7.86, −1.40; English, β = −4.66, 95%CI = −8.09, −1.23). IQ partially mediated the relationship between elevated blood lead concentrations and later school performance.

Conclusions

Findings support that blood lead concentrations in early childhood, even <10 µg/dL, have a long-term negative impact on cognitive development. The association between blood lead concentrations 8–10 µg/dL and cognitive development needs further study in Chinese children and children from other developing countries.

Regular breakfast consumption is associated with increased IQ in kindergarten children

BACKGROUND

Studies have documented a positive relationship between regular breakfast consumption and cognitive outcomes in youth. However, most of these studies have emphasized specific measures of cognition rather than cognitive performance as a broad construct (e.g., IQ test scores) and have been limited to Western samples of school-age children and adolescents. This study aims to extend the literature on breakfast consumption and cognition by examining these constructs in a sample of Chinese kindergarten-age children.

METHODS

This cross-sectional study consisted of a sample of 1269 children (697 boys and 572 girls) aged 6 years from the Chinese city of Jintan. Cognition was assessed with the Chinese version of the Wechsler preschool and primary scale of intelligence-revised. Breakfast habits were assessed through parental questionnaire. Analyses of variance and linear regression models were used to analyze the association between breakfast habits and IQ. Socioeconomic and parental psychosocial variables related to intelligence were controlled for.

RESULTS

Findings showed that children who regularly have breakfast on a near-daily basis had significantly higher full scale, verbal, and performance IQ test scores (all p<0.001) compared to children who "sometimes" have breakfast. This relationship persisted for VIQ (verbal IQ) and FIQ (full IQ) even after adjusting for gender, current living location, parental education, parental occupation, and primary child caregiver.

CONCLUSION

Findings may reflect nutritional as well as social benefits of regular breakfast consumption on cognition, and regular breakfast consumption should be encouraged among young children.

Sleep problems, fatigue, and cognitive performance in Chinese kindergarten children

OBJECTIVE

To examine sleep problems and fatigue and their associations with cognitive performance in Chinese kindergarten children.

STUDY DESIGN

A cross-sectional analysis of baseline data from Jintan Child Cohort Study was conducted, which includes a cohort of 1656 kindergarten children in Jintan City, Jiangsu Province, China. The sample used in the current study consisted of 1385 children (44.8% girls, mean age 5.72 [SD = 0.42] years) for whom data on sleep problems or cognitive performance were available. Child Behavior Checklist was used to measure child sleep problems and fatigue, and Wechsler Preschool and Primary Scale of Intelligence-Revised was used to assess child IQ.

RESULTS

Sleep problems were prevalent, ranging from 8.9% for difficulty maintaining sleep to 70.5% for unwilling to sleep alone. Other reported sleep problems were difficulty initiating sleep (39.4%), nightmares (31.6%), sleep talking (28%), sleeping less (24.7%), and sleep resistance (23.4%). Fatigue was also prevalent, with 29.6% of children reported to be overtired and 12.6% lack of energy. Children with difficulty maintaining sleep, sleep talking, sleep resistance, or nightmares scored 2-3 points lower in full IQ than children without sleep problems. Children reported to have fatigue scored 3-6 points lower in full IQ than those children without fatigue.

CONCLUSIONS

Sleep problems and fatigue are prevalent in Chinese kindergarten children. Furthermore, sleep problems and fatigue are associated with poor cognitive performance.

Sleep problems, fatigue, and cognitive performance in Chinese kindergarten children

OBJECTIVE

To examine sleep problems and fatigue and their associations with cognitive performance in Chinese kindergarten children.

STUDY DESIGN

A cross-sectional analysis of baseline data from Jintan Child Cohort Study was conducted, which includes a cohort of 1656 kindergarten children in Jintan City, Jiangsu Province, China. The sample used in the current study consisted of 1385 children (44.8% girls, mean age 5.72 [SD = 0.42] years) for whom data on sleep problems or cognitive performance were available. Child Behavior Checklist was used to measure child sleep problems and fatigue, and Wechsler Preschool and Primary Scale of Intelligence-Revised was used to assess child IQ.

RESULTS

Sleep problems were prevalent, ranging from 8.9% for difficulty maintaining sleep to 70.5% for unwilling to sleep alone. Other reported sleep problems were difficulty initiating sleep (39.4%), nightmares (31.6%), sleep talking (28%), sleeping less (24.7%), and sleep resistance (23.4%). Fatigue was also prevalent, with 29.6% of children reported to be overtired and 12.6% lack of energy. Children with difficulty maintaining sleep, sleep talking, sleep resistance, or nightmares scored 2-3 points lower in full IQ than children without sleep problems. Children reported to have fatigue scored 3-6 points lower in full IQ than those children without fatigue.

CONCLUSIONS

Sleep problems and fatigue are prevalent in Chinese kindergarten children. Furthermore, sleep problems and fatigue are associated with poor cognitive performance.

An increase of intelligence measured by the WPPSI in China, 1984-2006

Normative data for 5-6 year olds on the Chinese Preschool and Primary Scale of Intelligence (WPPSI) are reported for samples tested in 1984 and 2006. There was a significant increase in Full Scale IQ of 4.53 points over the 22 year period, representing a gain of 2.06 IQ points per decade. There were also significant increases in Verbal IQ of 4.27 points and in Performance IQ of 4.08 points.