Douglas K. Detterman

Scholastic Assessment or g? The Relationship Between the Scholastic Assessment Test and General Cognitive Ability

There is little evidence showing the relationship between the Scholastic Assessment Test (SAT) and g (general intelligence). This research established the relationship between SAT and g, as well as the appropriateness of the SAT as a measure of g, and examined the SAT as a premorbid measure of intelligence. In Study 1, we used the National Longitudinal Survey of Youth 1979. Measures of g were extracted from the Armed Services Vocational Aptitude Battery and correlated with SAT scores of 917 participants. The resulting correlation was .82 (.86 corrected for nonlinearity). Study 2 investigated the correlation between revised and recentered SAT scores and scores on the Ravens Advanced Progressive Matrices among 104 undergraduates. The resulting correlation was .483 (.72 corrected for restricted range). These studies indicate that the SAT is mainly a test of g. We provide equations for converting SAT scores to estimated IQs; such conversion could be useful for estimating premorbid IQ or conducting individual difference research with college students.

Correlations of Mental Tests with Each Other and with Cognitive Variables Are Highest for Low IQ Groups.

Two studies showed an inverse relationship between ability level and correlations among IQ measures. Low IQ subjects showed much higher correlations than high IQ subjects. Intercorrelations of IQ subtests, correlations of cognitive ability measures with each other, and correlations of IQ with measures of cognitive abilities all displayed the same effect. In the first study, data from two experiments in which subjects took a battery of basic cognitive tasks and a standard IQ test were analyzed. Measures from the basic tasks correlated more highly in the low IQ group than in the high IQ group. In the second study, data from the WAIS-R and WISC-R standardization samples were divided into five ability groups. Average correlations among subtests were computed for each ability group. For both the WAIS-R and WISC-R, average subtest correlations were highest in the low ability group. Correlations declined systematically with increasing IQ. In both studies, correlations were found to be two times higher in low IQ groups than in high IQ groups.

Associations between Cognitive Abilities and Scholastic Achievement: Genetic Overlap but Environmental Differences:

Little is known about the genetic and environmental etiology of the association between specific cognitive abilities and scholastic achievement during the early school years. A multivariate genetic analysis of cognitive and achievement measures was conducted for 146 pairs of identical twins and 132 pairs of fraternal twins from 6 to 12 years of age. At the phenotypic level, measures of achievement were moderately correlated with specific cognitive abilities. A multivariate model including one general factor and specific factors in the genetic and environmental matrices indicated that the phenotypic relationship between achievement and cognition was mediated primarily by genetic influences. Genetic correlations among the cognitive and achievement tests ranged from .57 to .85, shared environment correlations were essentially zero, and specific environment correlations were low (.00 to .19). We conclude that there is substantial overlap between genetic effects on scholastic achievement and specific cognitive abilities. Performance on ability measures differs from that on achievement measures largely for environmental reasons.

A Quantitative Trait Locus Associated With Cognitive Ability in Children

Quantitative trait loci (QTLs) associated with general cognitive ability (g) were investigated for several groups of children selected for very high or for average cognitive functioning. A DNA marker in the gene for insulin-like growth factor-2 receptor (IGF2R) on Chromosome 6 yielded a significantly greater frequency of a particular form of the gene (allele) in a high-g group (.303; average IQ = 136, N = 51) than in a control group (.156; average IQ = 103, N = 51). This association was replicated in an extremely-high-g group (all estimated IQs > 160, N = 52) as compared with an independent control group (average IQ = 101, N = 50), with allelic frequencies of .340 and .169, respectively. Moreover, a high-mathematics-ability group (N = 62) and a high-verbal-ability group (N = 51) yielded results that were in the same direction but only marginally significant (p = .06 and .08, respectively).

Does "g" Exist?.

Abstract Is the nature of intelligence best understood as a single thing (“g”), or as a set of orthogonal variables? It is argued that a set of orthogonal variables is most likely to explain intelligence. Higher-order constructs like metacomponents, Executive Functioning and “g” are suggested to inevitably result from complex systems having interrelated parts. While such constructs may provide indices of the efficiency of such systems, they do not explain how the systems function. Further, neither parsimony, the pervasiveness of such constructs, nor biological reductionism provide adequate justification for invoking higher-order constructs as explanations of intellectual functioning.

The Fagan test of infant intelligence: A technical summary☆

Abstract The present article summarizes the most recent data on the psychometric properties of the Fagan test of Infant Intelligence. Following a brief discussion of the empirical basis of the Fagan test, a note on the theoretical rationale underlying the test, and a summary of the development of the test, the current status of the Fagan test is presented. The section on current status includes a description of the Fagan test, data and discussions on reliability, validity, and clinical utility, and notes on issues such as cross-cultural utility and affordability. The article concludes with a section on practical implications raised by the transfer of the Fagan test to professionals who are interested in high-risk infants.

DNA markers associated with high versus low IQ: The IQ quantitative trait loci (QTL) project

General cognitive ability (intelligence, often indexed by IQ scores) is one of the most highly heritable behavioral dimensions. In an attempt to identify some of the many genes (quantitative trait loci; QTL) responsible for the substantial heritability of this quantitative trait, the IQ QTL Project uses an allelic association strategy. Allelic frequencies are compared for the high and low extremes of the IQ dimension using DNA markers in or near genes that are likely to be relevant to neural functioning. Permanent cell lines have been established for low-IQ (mean IQ=82;N=18), middle-IQ (mean IQ=105;N=21), and high-IQ (mean IQ=130;N=24) groups and for a replication sample consisting of even more extreme low-IQ (mean IQ=59;N=17) and high-IQ (mean IQ=142;N=27) groups. Subjects are Caucasian children tested from 6 to 12 years of age. This first report of the IQ QTL Project presents allelic association results for 46 two-allele markers and for 26 comparisons for 14 multiple-allele markers. Two markers yielded significant (p<.01) allelic frequency differences between the high- and the low-IQ groups in the combined sample—a new HLA marker for a gene unique to the human species and a new brain-expressed triplet repeat marker (CTGB33). The prospects for harnessing the power of molecular genetic techniques to identify QTL for quantitative dimensions of human behavior are discussed.

What Is So Special about Special Education

There is nothing special about special education. Educational methods have not changed significantly in at least 2,500 years. IQ tests were developed to identify those in need of special education, with the intention of developing appropriate educational methods. Effective special educational methods have yet to be developed. IQ tests are diagnostic but not prescriptive. Effective special educational methods will not be developed until (a) individual differences in student characteristics beyond IQ scores are recognized and understood and (b) educators focus on specific and realistic goals for outcome.

Allelic Associations between 100 DNA Markers and High versus Low IQ.

For DNA markers in or near genes of neurological relevance, allelic frequencies were compared for groups of White children high and low in IQ in an attempt to identify specific genes responsible for the substantial heritability of IQ scores. We previously reported results for 60 DNA markers and we now describe results for 40 additional markers. One sample consisted of high- and low-IQ groups with average IQs of 130 (N = 24) and 82 (N = 18), respectively. A replication sample was more extreme, including groups with average IQs of 142 (N = 27) and 59 (N = 17). Three of the 40 markers yielded significant allelic frequency differences between the high- and low-IQ groups in the original sample. In the replication sample, two of these markers (alcohol dehydrogenase 5 and the beta polypeptide of nerve growth factor) yielded results in the same direction but were not significant. The third marker (EST00083), derived from a cDNA hippocampal library, was also significant in the replication sample. As described in another article (Skuder et al., 1995) in this issue, this marker was found to involve mitochondrial DNA (mtDNA) rather than nuclear DNA. The unexpected nature of this marker suggests caution in claiming that the replicated association for EST00083 is indeed a quantitative trait loci (QTL) for IQ until the association receives additional support. This study provides statistical power to detect associations that account for about 2% of the IQ variance in the population. We are currently obtaining samples four times larger that will provide statistical power to detect allelic associations that account for considerably less than 1% of the variance.

The causal factor underlying the correlation between psychometric g and scholastic performance

Abstract Structural equation models were fitted to covariances among 9 Cognitive Abilities Test (CAT) variables, 11 Wechsler Intelligence Scale for Children—Revised (WISC-R) subtest scores, and 3 Metropolitan Achievement Test (MAT) scaled scores, administered to a sample of 532 primary school children who participated in the Western Reserve Twin Project. The models were designed to test the hypothesis that factors representing basic cognitive processes, extracted from the nine CAT variables, were the main causal determinants for the observed correlation between psychometric g and scholastic performance, which were represented, respectively, by a general factor extracted from the WISC-R and a factor from the MAT. Structural relations between the CAT factors as the primary independent variables, psychometric g as a secondary independent variable, and scholastic performance as the dependent variables were estimated, and the R2 change indicating the higher-order shared variability between g and scholastic performance was evaluated. After the influence of a CAT general factor was controlled, the WISC-R general factor accounted for about 6% of the variability in the MAT scholastic factor, as opposed to as much as 30% of the zero-order variability shared by the two variables. The results were not seriously affected by the exclusion of nonchronometric measures of the cognitive tasks from the model, suggesting that individual differences in mental speed are a main causal factor underlying the observed correlation between general intelligence and scholastic performance in children between the ages of 6 and 13.