Arthur Jensen's (1998, 1999) new book, "The G-Factor: The Science of Mental Ability," examines the historical evolution of the g factor as well as many of the modern-day implications of this development for psychologists. The implications of his findings for school psychologists are discussed, as are suggestions for future research.
2. Jensen's first several chapters review the history of intelligence testing, beginning with the philosophical contribution of Plato and Aristotle, and continuing with a review of the work of Galton and the subsequent development of the first modern-day (Binet's) test of intelligence in 1905. Jensen proceeds by reviewing alternative conceptualisations of g and corresponding historical and modern-day theories of intelligence. Many currently available commercial tests of intelligence have been increasingly criticised for their lack of a strong theoretical foundation. Perhaps due to the recent popularity of theories of multiple intelligences, successive revisions of many IQ tests have evolved to measure increasing numbers of "intelligences". For example, the newest editions of both the Stanford Binet (Stanford Binet IV) and the Wechsler Intelligence Scale for Children-Third Edition (WISC-III) now claim to measure four intelligence "factors" without any corresponding change in the theories underlying the tests. Because it remains unclear how many "types" of intelligence are being measured by these scales, there currently exists marked disagreement among school psychologists regarding their level of diagnostic interpretability (Kush, 1996). Jensen's early chapters clearly point out the critical importance of the need for a greater alliance between theories of intelligence and tests of intelligence.
3. There is also considerable attention in the book to the distinction between measures of learning and measures of intelligence. This distinction is critical for school psychologists who assess children and make recommendations for remediation and interventions. Certainly, all children are capable of learning; however, their rates of and capacities for learning are not uniform and Jensen carefully and thoughtfully reviews the professional and public implications of this distinction. As Jensen correctly points out, no educator enjoys telling a parent that their child has a low IQ or is doing poorly in school; as a result, theories of multiple intelligence have become a popular alternative -- parents can now be told that while their child may be lacking in one type of intelligence, there remain many other types in which they can still excel. This egalitarian fallacy -- that all human subgroups are equal in traits measured by IQ tests -- is directly challenged by Jensen, and the limitations of theories of multiple intelligences are carefully reviewed. Success in school develops from the interaction between intelligence and learning and an appreciation of the distinction between what is genetic and what is learned from the environment is perhaps the greatest contribution of The G Factor.
4. For school psychologists, perhaps the most fundamental utility of an IQ test is the prediction of school success/failure or academic achievement. Commercial IQ tests, like the WISC-III, are often the best predictors of school success available to school psychologists, and many school psychologists have suggested that the term IQ-test be replaced with terminology with less "emotional baggage" such as School Success Indicator, or School Achievement Forecast. Most commercially available tests of intelligence are highly correlated (typically .55 to .65) with tests of achievement because their item content includes g-related tasks as well as tasks that are clearly reflective of environmentally learned material (e.g., How far is it from San Francisco to Paris?; What are the four seasons of the year?). While this combination of tasks-of-intelligence with tasks-of-learning improves the predictive power of commercial IQ tests, it also creates situations where school psychologists are often forced to defend IQ test questions that appear culturally loaded. Jensen's research suggests that reaction time and inspection time tasks are much purer measures of "true" intelligence and will offer school psychologists a more face-valid alternative to traditional commercial IQ tests. However, the result may come with a loss in predictive power and school psychologists may face the dilemma of choosing between more experimental measures of pure intelligence with weaker forecasting ability and traditional tests of intelligence which are contaminated with non g-related subtests but yield stronger correlations with academic achievement.
5. Attempts to improve the predictive power of commercial IQ tests (beyond g) have, for the most part, proven unsuccessful. For example, one attempt in school psychology that has gained recent popularity is the cross battery approach related to Cattell and Horn's notion of fluid (Gf) and crystallised (Gc) intelligence. Jensen correctly points out that it is not yet clear how the Gf factor is substantially distinct from the higher-order g factor; however, greater attention could have been given to the additional criticism that Gc may actually be a measure of achievement rather than intelligence. Psychologists continue to debate whether questions such as "If Katharine has 4 apples and eats one of them, how many will she have left?" are measures of intelligence (numerical reasoning) or measures of achievement (mathematics calculation). It should come as no surprise that an increased predictive validity coefficient is produced when this type of question occurs on both the predictor (IQ) as well as the criterion (achievement) measure. Greater attention to problems such as this would have strengthened the practical utility of the book.
6. Empirical evidence for comparable predictive validities of measures of g across ethnic groups is also carefully reviewed by Jensen, and continues to show that these measures are free of psychometric bias. The literature reviewed by Jensen describing subgroup similarities and differences in tasks of reaction time and inspection time will be particularly interesting for school psychologists. Additional research examining possible differential predictions of academic achievement from these reaction time and inspection time tasks, across developmental stages and across ethnic groups, also remain to be completed.
7. Despite the carefully outlined presentation supporting Jensen's claims for the importance of g, critics will undoubtedly continue to challenge his findings. Most proponents of the cultural test bias hypothesis, with the notable exception of Flynn (1987), tend to make these arguments from theoretical rather than data-driven positions. Although Jensen provides much evidence to refute many of these claims, several criticisms receive only minimal attention. Helms (1992), for example, argues that most g-related tasks are European centred, emphasising (among other things) "action orientation" and "competition". "African-centered" values, in contrast, emphasise "spirituality", "harmony" and "social time". Similarly, Ogbu (1994) has argued that research examining ethnic differences in IQ tests must recognise a distinction between voluntary or immigrant minorities and involuntary or nonimmigrant minorities. Ogbu suggests that voluntary and involuntary minorities develop different cognitive frames of reference toward many things, including IQ test performance, depending on whether they or their ancestors freely chose to come to their new country or were forced to emigrate.
8. These criticisms have important implications, and while Jensen does provide some rebuttals to these arguments (e.g., comparable factorial and predictive validities; p. 512), a more detailed response would certainly have proven beneficial to school psychologists, who are currently wrestling with this issue. Jensen would probably agree with Hull's (1988) belief that science (including psychology) works much like evolution, so that over time only the better data and better theories will survive. Despite our frequent frustration at the pace at which the test fairness debate is evolving (and often de-evolving), Jensen's book reminds us that ultimately psychology as a science must be supported by rigorous and empirically replicated research rather than politically correct propaganda.
9. Overall, Jensen's book has much to offer both practising and research oriented school psychologists. It represents a welcome and much needed contribution to the field and should become required reading for all advanced level, graduate students in school psychology.
Flynn, J. R. (1987). Race and IQ: Jensen's case refuted. In S. Modgil & C. Modgil (Eds.), Arthur Jensen: Consensus and controversy (pp. 221-232). New York: Falmer.
Helms, J. E. (1992). Why is there no study of cultural equivalence in standardised cognitive ability testing? American Psychologist, 47, 1083-1101.
Hull, D. L. (1988). Science as a process. Chicago: University of Chicago Press.
Jensen, A. R. (1980). Bias in mental testing. New York: Free Press.
Jensen, A. (1998). The g Factor: The Science of Mental Ability. Praeger
Jensen, A. (1999). Precis of: "The g Factor: The Science of Mental Ability" PSYCOLOQUY 10 (023). ftp://ftp.princeton.edu/pub/harnad/Psycoloquy/1999.volume.10/ psyc.99.10.023.intelligence-g-factor.1.jensen http://www.cogsci.soton.ac.uk/cgi/psyc/newpsy?10.023
Kush, J. C. (1996). Factor structure of the WISC-III for students with learning disabilities. Journal of Psychoeducational Assessment, 14, 32-40.
Ogbu, J. U. (1994). Culture and intelligence. In R. J. Sternberg (Ed.), Encyclopedia of human intelligence, Vol. 2 (pp. 328-338). New York: Macmillan.