Average IQ Scores Research Articles

School-level genetic variation predicts school-level verbal IQ scores: Results from a sample of American middle and high schools

Research has consistently revealed that average IQ scores vary significantly across macro-level units, such as states and nations. The reason for this variation in IQ, however, has remained at the center of much controversy. One of the more provocative explanations is that IQ across macro-level units is the result of genetic differences, but empirical studies have yet to examine this possibility directly. The current study partially addresses this gap in the literature by examining whether average IQ scores across thirty-six schools are associated with differences in the allelic distributions of dopaminergic polymorphisms across schools. Analysis of data drawn from subjects (ages 12–19 years) participating in the National Longitudinal Study of Adolescent Health provides support in favor of this perspective, where variation in school-level IQ scores was predicted by school-level genetic variation. This association remained statistically significant even after controlling for the effects of race.

IQ IN THE PRODUCTION FUNCTION: EVIDENCE FROM IMMIGRANT EARNINGS

We show that a country’s average IQ score is a useful predictor of the wages that immigrants from that country earn in the United States, whether or not one adjusts for immigrant education. Just as in numerous microeconomic studies, 1 IQ point predicts 1% higher wages, suggesting that IQ tests capture an important difference in cross‐country worker productivity. In a cross‐country development accounting exercise, about one‐sixth of the global inequality in log income can be explained by the effect of large, persistent differences in national average IQ on the private marginal product of labor. This suggests that cognitive skills matter more for groups than for individuals. (JEL J24, J61, O47)

Local vs. global approaches to reproducing the Rey Osterrieth Complex Figure by children, adolescents, and adults with high-functioning autism.

Individuals with autism have an atypical pattern of visual processing. Various studies have provided evidence that individuals with autism perceive the details of stimuli before the gestalt, the reverse of the typical pattern of visual processing. This study used the Rey Osterreith Complex Figure (ROCF) task and an objective scoring system to examine local/global processing approaches to its reproduction in 37 individuals diagnosed with high-functioning autism (HFA) compared to 49 age-, IQ-, and gender-matched typically developing controls (TD). The sample was divided into children (aged 8-14 years) and adolescents/adults (aged 15-47 years) to assess age effects. Results showed no difference in overall performance on the ROCF between HFA and TD children. TD participants displayed improved organizational and planning skills with age and a shift to global processing approaches, but there were no differences in performance between children and adolescents/adults with HFA. There was no evidence of enhanced local processing in either HFA group. These findings suggest that HFA individuals with average IQ scores do not have the clinically demonstrable evidence of the enhanced local processing thought to reflect increased local brain connectivity in more severely autistic individuals. The deficient global processing of the HFA adults reflects dependence of performance on impaired strategic problem-solving abilities, which has been demonstrated to result from under development of neural connectivity between visuo-spatial and frontal brain regions in HFA adults.

Commentary: Environmental Influences: Issues of Timing and Type

Long-term neurodevelopmental outcome is frequently considered the benchmark in determining the natural sequelae of biologic risks, or the efficacy of various medical interventions in infants born at extremely low birth weight (ELBW; Aylward, 2005). Initially, primary emphasis in outcome studies was placed on major disabilities: moderate/severe intellectual disabilities, sensorineural hearing loss/blindness, cerebral palsy, and epilepsy. However, increasing numbers of ‘‘non-disabled’’ survivors subsequently were found to display problems at later ages. These high prevalence/low severity dysfunctions include learning disabilities (written expression, math, reading), borderline/low average IQ scores, neuropsychological deficits (e.g., visual motor integration, executive function) and behavior problems (Aylward, 2002, 2005). These dysfunctions occur in 50–70% of those born at ELBW, and 70% of these children require special education services (Taylor, Klein, & Hack, 2000). High prevalence/low severity dysfunctions tend to aggregate and work synergistically (Aylward, 2002, 2005). While major disabilities can be identified early, high prevalence/low severity dysfunctions often become more obvious as the child grows older. Therefore, the social, ethnic, and educational backgrounds of parents have a greater likelihood of influencing these problems in longitudinal follow-up. This situation has an impact on casual inferences by introducing risk and protective factors as mediators and moderators of ELBW and later outcomes (Rose, Holmbeck, Millstein Coakley, & Franks, 2004). Environment contains ‘‘process’’ (proximal aspects experienced most directly; mother–infant interactions, stimulation in the home) and ‘‘status’’ features (distal or broader, involving aspects that the child experiences more indirectly; socioeconomic status, neighborhood) (Aylward, 1992). Process or proximal environmental variables are more predictive early on, while status factors are more influential later (Brooks-Gunn, Duncan, & Aber, 1997). Sociodemographic factors are associated with verbal, academic, and general cognitive abilities; both biomedical and environmental risks affect learning disorders (Aylward, 1992, 2002). Brofenbrenner’s ‘‘microsystem’’ incorporates these factors and includes various aspects of the immediate environment (family, school, peer group, neighborhood, and childcare milieu). The paper by Andreias et al. (2009) has many strengths: a control group, use of a theoretic model, a multilevel modeling approach, adequate follow-up compliance, and inclusion of various measures of the microsystem. At 8 years of age, family environment had a greater influence on academic achievement than did neighborhood characteristics (poverty rate, high school dropout rate). Neighborhood had an effect over and above that of individual and family variables, indicating a unique contribution. However, the model that included individual, family, and neighborhood factors accounted for the most explained variance. The current data raise the possibility of an evolving

Valproate Linked to Increased Prenatal Risks

Back to table of contents Previous article Next article Clinical & Research NewsFull AccessValproate Linked to Increased Prenatal RisksJun YanJun YanSearch for more papers by this authorPublished Online:15 May 2009https://doi.org/10.1176/pn.44.10.0023Valproate, an epilepsy drug also used to treat bipolar disorder, is linked to lower IQ scores at age 3 in children exposed to the drug before birth than in children whose mothers took other antiepileptic drugs during pregnancy, a study published in the April 4 New England Journal of Medicine showed.From 1999 to 2004, U.S. and U.K. researchers enrolled 303 pregnant women with epilepsy who were taking lamotrigine, phenytoin, carbamazepine, or valproate in a prospective, observational study known as the Neurodevelopmental Effects of Antiepileptic Drugs study. The researchers conducted follow-up assessments, especially in terms of neurological development, in the children. Women who were not taking any antiepileptic drugs during pregnancy were not included.The average IQ score of 3-year-old children who had in utero exposure to valproate was 92, which was statistically significantly lower than that of children exposed to lamotrigine (average IQ 101), phenytoin (99), or carbamazepine (98). The comparisons among lamotrigine, phenytoin, and carbamazepine were not statistically different. The authors also found a dose-dependent relationship between valproate and IQ score.That valproate exposure carries a higher risk of birth defects than other antiepileptics, such as lamotrigine and carbamazepine, is not new knowledge, Torbjorn Tomson, M.D., a professor of clinical neuroscience at the Karolinska Institute in Sweden, pointed out in an editorial. The worthwhile discovery of this study was the differential effects on children's long-term cognitive development associated with various antiepileptics. This was the largest prospective study so far on the effects of antiepileptics on cognitive development.This study was reported in several media outlets, including the New York Times and the Associated Press, with broad headlines such as“ I.Q. Harmed by Epilepsy Drug in Utero,” without clearly presenting the context that the study was a comparison between valproate and other antiepileptic drugs.Untreated epilepsy, as well as untreated bipolar disorder, poses a significant risk of harm to pregnant women and their fetuses. For many pregnant patients, stopping medication is not an option. Therefore, accurately describing the different risks among drugs in the same class is critically important for physicians and patients. The authors concluded that valproate should not be used as a first-line treatment for women who are pregnant or may become pregnant. In addition, “discussion of the risks of valproate should be balanced with consideration of the risks of uncontrolled seizures,” Tomson recommended.An abstract of “Cognitive Function at 3 Years of Age After Fetal Exposure to Antiepileptic Drugs” is posted at<content.nejm.org/cgi/content/short/360/16/1597>.▪ ISSUES NewArchived

Neurocognitive profile in children with fetal alcohol spectrum disorders

The question of whether children with fetal alcohol spectrum disorders (FASD) exhibit a unique neurocognitive profile has received considerable attention over the past three decades. The identification of a syndrome-specific neurocognitive profile would aid in diagnosing prenatally exposed children with cognitive deficits who do not exhibit clinically discernable physical anomalies. The current review of the literature, therefore, focuses on the studies of higher-order cognitive skills in children with FASDs with a view towards delineating a pattern of cognitive functioning. Researchers have documented that children with FASDs show diminished intellectual functioning, with average IQ scores falling within the borderline to low average ranges. Slow information processing and disturbances of attention have been observed from infancy through adulthood in individuals with FASDs. Clinical and experimental reports on individuals with FASD have documented marked deficits in executive functioning, particularly in tasks that involve holding and manipulating information in working memory. Studies examining specific domains of cognitive functioning such as language, visual perception, memory and learning, social functioning, and number processing in individuals with FASDs have revealed performance decrements associated with increased task complexity. The above findings converge on the conclusion that children with FASDs have a generalized deficit in the processing and integration of information. We recommend the study of developmental trajectories of both elementary and higher-order functions in future research on FASD to elucidate the development of this cognitive profile.

IQ and non-clinical psychotic symptoms in 12-year-olds: results from the ALSPAC birth cohort

BackgroundNon-clinical psychotic symptoms appear common in children, but it is possible that a proportion of reported symptoms result from misinterpretation. There is a well-established association between pre-morbid low IQ score and schizophrenia. Psychosis-like symptoms in children may also be a risk factor for psychotic disorder but their relationship with IQ is unclear.AimsTo investigate the prevalence, nature and frequency of psychosis-like symptoms in 12-year-old children and study their relationship with IQ.MethodLongitudinal study using the Avon Longitudinal Study of Parents and Children (ALSPAC) birth cohort. A total of 6455 children completed screening questions for 12 psychotic symptoms followed by a semi-structured clinical assessment. IQ was assessed at 8 years of age using the Wechsler Intelligence Scale for Children (3rd UK edition).ResultsThe 6-month period prevalence for one or more symptoms was 13.7% (95% CI 12.8–14.5). After adjustment for confounding variables, there was a non-linear association between IQ score and psychosis-like symptoms, such that only those with below average IQ score had an increased risk of reporting such symptoms.ConclusionsNon-clinical psychotic symptoms occur in a significant proportion of 12-year-olds. Symptoms are associated with low IQ and also less strongly with a high IQ score. The pattern of association with IQ differs from that observed in schizophrenia.

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A multidisciplinary approach to the management of individuals with fragile X syndrome

Fragile X syndrome (FXS) is the most common inherited form of intellectual disability. Since the identification of the responsible gene (FMR1) and its protein (FMRP), there has been enormous progress in both clinical and pathogenetic research on the neurobehavioural aspects of the condition. However, studies regarding other medical problems anticipated in individuals with FXS are limited. A multidisciplinary study evaluating various causes of morbidity in the same group has not been published yet. Twenty-four boys with FXS full mutation were recruited out of a larger group of 103 diagnosed in one centre over the past 10 years. Ear nose and throat, eye and cardiac examinations were performed in addition to routine cognitive, behavioural, neurological and speech and language assessments. The average IQ score was 49.8 +/- 20 (range 25-90). There were four patients (18%) with IQ above 70. Using DSM-IV, attention deficit hyperactivity disorder was diagnosed in five boys out of 22 examined (23%), while 32% were diagnosed with pervasive developmental disorder. The seizure frequency was 17%. A psychiatric disorder was diagnosed in six out of eight boys with electroencephalogram abnormalities (75%). Minimal conductive hearing loss was found in five (5/22) patients. There was significant delay in both expressive and receptive language skills. Ocular findings were refractive errors (13%) and strabismus (4.4%). Mitral valve prolapsus (MVP) was observed in 3/22 (13.7%) patients and aortic annulus dilatation was present in 2/22 (9%) patients. Frequency of psychiatric diagnoses made with DSM-IV were in parallel to those reported in the literature. Comorbidity of seizures and psychiatric disorders was noteworthy. The percentage of 'high-functioning' full mutation males supports the previous observations. Ear nose and throat and eye examination revealed remarkably lower prevalence of abnormal findings than reported. MVP was slightly less frequent compared with the single study in the literature. Age at the time of examination had an effect on the outcome of cardiac evaluation. These findings will guide us in future management of the group of patients followed in our institution. The protocol applied provides an applicable outline for multidisciplinary institutional settings dealing with individuals with FXS.

Executive functions in school-age children born very prematurely

Background School-age preterm children are at risk for cognitive difficulties including Executive Dysfunction and low average IQ. Aim The aim of this study was to determine the performance of very preterm, school-age children on three components of Executive Function (EF), two components of Executive Attention and a measure of IQ. Study design Cross-sectional, independent samples comparison. Methods A UK sample of 40 very preterm (< 32 weeks gestational age, Mean 28.43, SD 2.41) children and 41 term born control children aged between 6 and 12 years (mean ages 8 years 5 months in both groups) was assessed on IQ, EF (inhibition, working memory and set shifting) and attention (sustained and selective). Between group comparisons were made using multivariate analysis of variance and covariance. Results Multivariate analyses indicated that preterm children scored significantly lower than their term born peers across Executive Function and executive attention tasks. As expected, the preterm group achieved IQ scores at the low end of the average range. Univariate analyses indicated some difficulties with shifting and inhibition components of EF, although covariate analysis revealed that only shifting was independent of IQ. Conclusions Preterm children showed mild executive function and executive attention difficulties in the context of average IQ scores. The findings highlight the benefit of using multivariate assessments of executive skills rather than general intellectual outcome alone, to obtain a better distinction of the specific cognitive weaknesses associated with preterm birth.

Effects of Prelinguistic Communication Levels on Initiation and Repair of Communication in Children With Disabilities

This study examined the effects of expressive and receptive language levels on initiated and repaired communication acts by prelinguistic children with developmental disabilities. In this descriptive study, participants were 45 children between the ages of 3 and 6 years who had severe delays in expressive communication. Some children communicated with 12 or fewer spoken words; others communicated exclusively with gestures and vocalizations. Participants also had delays in receptive language, and 41 of the 45 had below average IQ scores. The children participated in a scripted interaction with examiners that was designed to provide opportunities to initiate requests and comments, and to repair communication breakdowns. Videotapes of these interactions were later coded for analysis. Regression models indicated that differences in children's expressive communication levels and receptive language scores significantly predicted children's commenting communication acts during the scripted interaction, even after the authors accounted for child IQ. Expressive communication level was also a significant predictor of initiated requests when the authors controlled for IQ. Expressive communication level contributed to the variance in children's repairs following communication breakdowns; however, this contribution was not significant. Differences in levels of prelinguistic communication development predict commenting abilities in children with developmental disabilities but do not appear to predict likelihood to repair communication breakdowns.

Phenylalanine hydroxylase deficiency: intelligence of patients after early dietary treatment.

Neonatal screening for hyperphenylalaninemia (HPA) has been performed in Taiwan for more than 20 years. In this paper, we studied 21 cases of HPA caused by phenylalanine hydroxylase (PAH) deficiency. These patients were detected by a single newborn screening center over ten-years, and the incidence was one in 63,690. According to the initial plasma phenylalanine levels, four of the 21 patients belonged to classical phenylketonuria (PKU), seven were mild PKU, and ten were mild HPA. They commenced diet control at the age of 47 +/- 22 (17-106) days. Fourteen patients completed IQ tests, three of the 14 patients having classical PKU, five having mild PKU, and six having mild HPA. Their average IQ scores were within normal ranges (full-scale IQ 98 +/- 14, verbal IQ 92 +/- 8, and performance IQ 104 +/- 19), but patients with classical PKU tended to have lower IQ scores than other patients. Since classical PKU is rare in Taiwan, further studies including detailed neuropsychological tests will be required to evaluate the effect of treatment in this group of patients.

School-Age Outcomes for Early Intervention Participants Who Experienced Intraventricular Hemorrhage and Low Birth Weight

This study examines long-term outcomes for 82 children with intraventricular hemorrhage (IVH) and low birth weight (LBW; 530-2,420 g) who participated in at least 18 months of early intervention. Outcomes were assessed at 71/2 and 81/2 years of age; the majority had average development and IQ scores. Grade III and IV IVH youngsters had lower developmental scores. Participants scored quite well compared to earlier IVH infant samples, suggesting early intervention and improved medical technology contribute improvements. Analyses demonstrated that, even in this medically compromised population, home environment characteristics were closely related to older verbal development.

Speech and language skills and cognitive functioning in children with Apert syndrome: a pilot study.

There are few studies that report findings on the speech and language characteristics of Apert syndrome and little is known about the cognitive profile of the syndrome. The current study addresses this gap and explores speech, language, resonance/voice, attention oro-motor and cognitive skills in a group of 10 children (4;1-5;11) with Apert syndrome. The speech and language battery included: the CELF-Pre-school, the PLS-3, the Vocal Profile Analysis, GOS.SP.ASS, PACS; and the Brodsky Drooling Scale. Subscales of the BAS II-Early Years Version were used to assess cognition. Data were also collected on other factors that could influence developmental outcome such as audiological history and management; occlusion/dentition; respiratory problems and management; neuroanatomical abnormalities; the number and nature of cranial surgeries; and the occurrence of raised intracranial pressure. All children for whom a Performance IQ was obtained (n = 8) had abilities within the average range and IQ scores were considerably higher than those reported in previous studies. Eight children had moderate or severe language difficulties and expressive language difficulties were the most frequent. These language difficulties were not associated with a general cognitive deficit. All the children had problems with attention, speech and oro-motor skills. Nine had abnormal voice. In addition, a range of other associated factors that could affect functioning were identified. The discrepancies between the current study and previous investigations are outlined. Parameters for assessment are considered. The implications of these findings for valid assessments of children with Apert syndrome are discussed. Multidisciplinary assessment of children with Apert syndrome across a broad range of dimensions is recommended to obtain a profile of each child's strengths and weaknesses to ensure that appropriate educational placements and early interventions are implemented. Considering patterns of development over time at key ages is also argued to be of central importance.

Preliminary Real-World Evidence That Average Human Intelligence Really is Rising

Average IQ score has been rising for several decades but researchers dispute whether population intelligence really is increasing. Clear real-world evidence of a rise may settle the issue. I first examined the domain of chess, where performance can be readily measured and tracked over decades and people of all ages compete. The young increasingly have dominated the game since the 1970's, outperforming older players at progressively earlier ages. The median age of the top 50 players dropped from 38 years old in the 1970's to 29 in 1995, and the proportion aged under 25 more than doubled. The median age of the top 10 dropped from the late-30's in the 1970's to the mid-20's in the 1990s. The median age of world championship contenders dropped from 37 in 1971 to just 26 in 1994. The Soviet team which won the 1970 Chess Olympiad had a median age of 40 and the Russian team which won the 1998 Olympiad had a median age of 22.5. The longstanding record for youngest grandmaster, set in 1958, has been broken four times since 1991. I also looked at patent and educational statistics, which have been used to suggest that intelligence is not rising. Number of U.S. patents granted largely rose from 1963 to 1996. SAT test scores overall largely have fallen from 1951, but possibly for many reasons. The chess data are the first real-world evidence that population intelligence really may be rising.

Relationship among genotype, biochemical phenotype, and cognitive performance in females with phenylalanine hydroxylase deficiency: report from the Maternal Phenylketonuria Collaborative Study.

To examine the relationship of phenylalanine hydroxylase (PAH) genotypes to biochemical phenotype and cognitive development in maternal phenylketonuria (PKU). PAH gene mutations were examined in 222 hyperphenylalaninemic females enrolled in the Maternal PKU Collaborative Study (MPKUCS). A total of 84 different mutations were detected, and complete genotype was obtained in 199 individuals. Based on previous knowledge about mutation-phenotype associations, 78 of the mutations could be assigned to one of four classes of severity (severe PKU, moderate PKU, mild PKU, and mild hyperphenylalaninemia [MHP]). Then, 189 MPKUCS subjects were grouped according to the various combinations of mutation classifications. The sample sizes were large enough for statistical testing in four groups with at least one mutation that completely abolishes enzyme activity. These patients are considered functionally hemizygous. The biochemical phenotype predicted from the genotype in functionally hemizygous patients was related significantly to the assigned phenylalanine level. Cognitive performance (IQ) was also significantly related to genotype. The IQ of PAH-deficient mothers with a severe PKU mutation in combination with a MHP mutation or a mild PKU mutation was 99 and 96, respectively, whereas the IQ of PKU mothers with two severe PKU mutations or with one severe and one moderate PKU mutation was 83 and 84, respectively. Of the patients with PKU, 92% had been treated during childhood. Those who were untreated or treated late had lower than average IQ scores for their group of mutation combinations. Females with moderate or mild PKU who were treated early and treated for >6 years showed IQ scores 10 points above average for their group. The reproductive outcome in maternal phenylketonuria is dependent on prenatal metabolic control and postnatal environmental circumstances. Both factors depend on the intellectual resources of the mother with PKU. The significant relationship among genotype, biochemical phenotype, and cognitive performance observed in the present study is of importance for the development of an optimal strategy for future treatment of females with PKU who plan pregnancy.

Mitochondrial DNA marker EST00083 is not associated with high vs. average IQ in a German sample

In a recent report in this journal (Plomin & Petrill, 1997), a mitochondrial DNA marker (EST00083) yielded significant associations with high vs. low IQ in two population-based samples of children in the U.S. The present study tested this allelic association for German adults with high vs. average IQ scores. The high IQ adults ( N=47) were members of Mensa, an organization whose membership criterion is an IQ score above 130. Their EST00083 allelic frequencies were compared to the allelic frequencies for a control group of adults ( N=77) whose IQ scores were less than 110 as estimated from short-term memory and speed-of information-processing tests. Although the differences between the two studies are considerable, the present results do not provide support for the hypothesis that EST00083 is associated with high IQ.

Juveniles' understanding of trial-related information: are they competent defendants?

There exists a national trend lowering the age to transfer children facing serious charges to adult court for trial. This study examined juvenile offenders' understanding of factual information about trials. Juveniles ages 11 through 16 experiencing their first institutional placement were administered a competence to stand trial screening measure, shown an educational videotape, and readministered the measure. Findings suggest that a majority do not have sufficient understanding for meaningful participation in their trials. Special care appears warranted with juveniles ages 13 and under, and juveniles with low average or below average IQ scores. Further, substantial training may be necessary for some juvenile offenders.

Intellectual impairment in children exposed to polychlorinated biphenyls in utero.

In utero exposure to polychlorinated biphenyls, a ubiquitous environmental contaminant, has been linked to adverse effects on neurologic and intellectual function in infants and young children. We assessed whether these effects persist through school age and examined their importance in the acquisition of reading and arithmetic skills. We tested 212 children, recruited as newborns to overrepresent infants born to women who had eaten Lake Michigan fish contaminated with polychlorinated biphenyls. A battery of IQ and achievement tests was administered when the children were 11 years of age. Concentrations of polychlorinated biphenyls in maternal serum and milk at delivery were slightly higher than in the general population. A composite measure of prenatal exposure was derived from concentrations in umbilical-cord serum and maternal serum and milk. Prenatal exposure to polychlorinated biphenyls was associated with lower full-scale and verbal IQ scores after control for potential confounding variables such as socioeconomic status (P = 0.02). The strongest effects related to memory and attention. The most highly exposed children were three times as likely to have low average IQ scores (P <0.001) and twice as likely to be at least two years behind in reading comprehension (P = 0.03). Although larger quantities of polychlorinated biphenyls are transferred by breast-feeding than in utero, there were deficits only in associated with transplacental exposure, suggesting that the developing fetal brain is particularly sensitive to these compounds. In utero exposure to polychlorinated biphenyls in concentrations slightly higher than those in the general population can have a long-term impact on intellectual function.

Concurrent validity of a WAIS—R seven-subtest short form in patients with brain impairment.

The concurrent validity of a Wechsler Adult Intelligence Scale-Revised (WAIS-R) seven-subtest short form was examined in 138 patients with closed-head injuries and 49 patients with presumed dementia. In patients with closed-head injuries, the average short form IQ score was within 1 point of the actual Verbal, Performance, and Full Scale IQ (VIQ, PIQ, and FSIQ) scores. The validity coefficients for these patients ranged from.90 to.95. In patients with presumed dementia, the short form underestimated the average VIQ by nearly 5 points and the average FSIQ by 3.5 points. However, the validity coefficients for these patients were uniformly high (.91 to to.95 ). Examination of the frequency distributions revealed that there was a percentage of patients whose short form IQs and actual IQs were highly discrepant. Research designed to determine the variables that reduce the accuracy of the short form in clinical populations is needed.