Arthur R. Jensen

Reaction Time and Psychometric g

Nearly 120 years ago, Sir Francis Galton expressed a theoretical preconception or intuition which most people - certainly most present-day psychologists - would regard as highly counter-intuitive, namely, the notion that reaction time (RT) is related to intelligence. The common reactions of disbelief to this notion express the view that nothing as simple, trivial, and nonintellectual as RT could possibly reflect anything as subtle, complex, and mysterious as human intelligence, and it is remarked that the most highly intelligent persons often appear to be slow but deep thinkers. In much of popular thought, speed of mental action implies superficiality; slowness, profundity.

Reaction Time, Movement Time, and Intelligence

Speed of information processing is measured in terms of reaction time (RT) and movement time (MT) to five stimulus displays which differ in the amount of information transmitted, over a range from 0 to 3 bits of information. RT, but not MT, increases as a linear function of the number of bits in the stimulus display. RT and MT show reliable individual differences which are significantly correlated with intelligence as measured by Ravens Standard Progressive Matrices.

THIRTY YEARS OF RESEARCH ON RACE DIFFERENCES IN COGNITIVE ABILITY

The culture-only (0% genetic–100% environmental) and the hereditarian (50% genetic–50% environmental) models of the causes of mean Black–White differences in cognitive ability are compared and contrasted across 10 categories of evidence: the worldwide distribution of test scores, g factor of mental ability, heritability, brain size and cognitive ability, transracial adoption, racial admixture, regression, related life-history traits, human origins research, and hypothesized environmental variables. The new evidence reviewed here points to some genetic component in Black–White differences in mean IQ. The implication for public policy is that the discrimination model (i.e., Black–White differences in socially valued outcomes will be equal barring discrimination) must be tempered by a distributional model (i.e., Black–White outcomes reflect underlying group characteristics).

What is a good g

We have examined the stability of psychometric g, the general factor in all mental ability tests or other manifestations of mental ability, when g is extracted from a given correlation matrix by different models or methods of factor analysis. This was investigated in simulated correlation matrices, in which the true g was known exactly, and in typical empirical data consisting of a large battery of diverse mental tests. Theoretically, some methods are more appropriate than others for extracting g, but in fact g is remarkably robust and almost invariant across different methods of analysis, both in agreement between the estimated g and the true g in simulated data and in similarity among the g factors extracted from empirical data by different methods. Although the near-uniformity of g obtained by different methods would seem to indicate that, practically speaking, there is little basis for choosing or rejecting any particular method, certain factor models qua models may accord better than others with theoretical considerations about the nature of g. What seems to us a reasonable strategy for estimating g, given an appropriate correlation matrix, is suggested for consideration. It seems safe to conclude that, in the domain of mental abilities, g is not in the least chimerical. Almost any g is a “good” g and is certainly better than no g.

Inspection Time and Intelligence: A Meta-Analysis

A meta-analysis of research on the relationship between inspection time (IT) and intelligence (IQ) was performed to: (1) determine whether a nonzero relationship between IT and IQ exists, (2) estimate the size of this relationship if it exists, and (3) test whether IT is ontogenetically related to g. Separate meta-analyses were initially conducted for results of studies using measures of general IQ, performance IQ, and verbal IQ for studies using samples of adults, children, and the mentally retarded. They were first conducted on the published (uncorrected) correlations. Following this, the resultant values were corrected for the extraneous effects of the artifacts (viz., sampling error, error of measurement, and range variation) and the meta-analyses were repeated. Results of these meta-analyses indicate that IT is related (negatively) to IQ, at least with measures of general IQ and performance IQ. For adults, with general measures of IQ, this correlation is about −.54, after correction for the effects of artifactual sources of error (−.30 prior to correction). IT, however, also appears to measure other factors besides g, possibly perceptual organization, which is reflected in the higher relationship of IT to performance measures of IQ. Finally, the theory that IT is ontogenetically related to IQ does not receive support. Rather, results of this study suggest that the degree of the IT-IQ relationship is relatively constant across age, at least through the range of ages tested in the literature.

Race, social class and ability patterns on the WISC-R

The national standardization sample of whites and blacks on the Wechsler Intelligence Scale for Children—Revised (WISC-R) was the basis for a detailed analysis of the psychometric nature of racial and social class differences on the original 13 subscales of the WISC-R. The profiles of subtest scores of whites and blacks were compared directly and also after the racial groups were statistically equated on Full Scale IQ (FSIQ). Under the latter condition, the races differ only very slightly, although significantly, on some of the subtests, in ways generally contrary to popular expectations. The profile of white-black differences on the WISC-R subtests is markedly different, and negatively correlated with, the profiles of social class differences within each racial group, indicating that the pattern of racial differences is not explainable in terms of the difference in the average socio-economic status (SES) of blacks and whites. A Schmid-Leiman orthogonalized hierarchical factor analysis yields virtually identical factor structures and highly congruent factor loadings on the subtests for whites and blacks. Analysis of factor scores shows that by far the largest proportion of the variance between races is attributable to the general factor (g) common to all the subtests, whereas the group factors (verbal, performance and memory) contribute only minutely to the interracial variance. Hence the white-black differences on the diverse subtests of the WISC-R, and in the Full Scale IQ, are interpreted primarily as a difference in Spearmans g, rather than as differences in the more specific factors peculiar to particular content, knowledge, acquired skills or type of test. However, some slight but significant differences in patterns of ability also occur that are independent of g.

THE IMPORTANCE OF INTRAINDIVIDUAL VARIATION IN REACTION TIME

Abstract Individual differences in the trial-to-trial variability of reaction time (RT), indexed by the standard deviation of the individuals RTs over n trials (RTSD), generally has a larger negative correlation with psychometric g than does the median RT (RTmd) over n trials. Large data sets are brought to bear on the question of whether RTmd and RTSD, which are highly correlated, reflect one and the same source of variance, but with different reliability and validity for predicting g, or represent independent processes. Several lines of evidence consistently lead to the conclusion that RTmd and RTSD, though having a substantial proportion of their variance in common even when measured separately in experimentally independent sets of RT trials, also have significant independent components of variance, each of which is correlated with psychometric g. Hypotheses about the neurophysiological basis of individual differences in the independent components of RTmd and RTSD are discussed.

g: Artifact or reality?☆

The highest common factor in any large and diverse collection of mental tests is measured by means of factor analysis, and is conventionally labeled psychometric g (for general ability). The g factor, which is highly correlated across even quite different batteries of tests, provided the tests are fairly numerous and varied, reflects the empirical fact of positive manifold, that is, positive correlations between all mental tests. After briefly explicating the general psychometric conditions and factor analytic methods for the measurement of g, this article addresses the theoretically important question of whether g is merely an artifact of the method of constructing psychometric tests and the mathematical operations of factor analysis or whether it has an authentic claim to represent some natural phenomenon that exists independently of psychometrics and factor analysis. Several lines of evidence which refute the argument that g is a methodological artifact are presented. The g factor, far more than any other linearly independent sources of variance in psychometric tests, is correlated with various phenomena that are wholly independent of both psychometrics and factor analysis, such as the heritability of test scores, familial correlations, the effects of inbreeding depression and of hybrid vigor, evoked electrical potentials of the brain, and reaction times to elementary cognitive tasks which have virtually no intellectual content. This evidence of biological correlates of g supports the theory that g is not a methodological artifact but is, indeed, a fact of nature. However, the causal nature of g itself is not yet scientifically established. That goal must await further advances in neuroscience.

Individual and group differences in intelligence and speed of information processing

Summary-A battery of eight different reaction time (RT) tests, measuring the speed with which individuals perform various elementary cognitive processes, and a group test of scholastic aptitude (the Armed Services Vocational Aptitude Battery, ASVAB) were given to 50 black and 56 white male vocational college students. The regression of the general factor scores of the ASVAB on the RT measures yielded a shrunken multiple correlation of 0.465. Although discriminant analyses, when applied separately to the ASVAB subtests and to the RT variables, showed highly comparable overall discrimination (over 70% correct classification) between the black and white groups, factor scores derived from the general factor (labeled ‘speed of information processing’) of the RT battery show only about one-third as large a mean black-white difference as the mean group difference on the general factor scores derived from the ASVAB. Comparisons were also made between the 106 vocational college students and 100 university students of higher average academic aptitude who had previously been tested on the same RT batter; IVernon, 1983a). These ErouDs showed marked differences on the RT variables. the largest differences occurring on the tests that required more complex cognitive processing. The more complex RT tests also correlate most highly with the psychometric measures of ability within each group. The results are consistent with the hypothesis that individual differences and the mean differences between groups in psychometric abilities and scholastic achievement are related to differences in the speed of information processing as measured in elementary cognitive tasks.

Chronometric analysis of intelligence

Measurements of various parameters derived from different reaction time (RT) paradigms are found to be correlated with psychometric measurements of general mental ability. Such RT-derived measurements, when combined in a multiple regression equation, predict some 50 per cent or more of the variance in IQ or g. This relationship of IQ or g to RT parameters indicates that our standard IQ tests tap fundamental processes involved in individual differences in intellectual ability and not merely differences in specific knowledge, acquired skills, or cultural background.