The rising curve: Long-term gains in IQ and related measures. (Book Reviews).

Neisser, U. (Ed.). (1998). The rising curve: Long-term gains in IQ and related measures. Washington, DC: American Psychological Association (415 pp., $27.97 hb, ISBN 1-55798-503-0).

Ulric Neisser's edited volume The Rising Curve: Long-term Gains in IQ and Related Measures addresses three issues: gains on intelligence tests, the narrowing gap in school achievement between Blacks and Whites, and the hypothesis of dysgenic trends in intelligence. Half of the book is dedicated to the first issue, which is seen by the editor and Howard Gardner (on the book jacket) as providing a serious challenge to the findings of The Bell Curve. The argument is that, contrary to notion of "fixed intelligence," IQs worldwide have shown a dramatic increase over the past century. The basic evidence for this is studies of changes in score distributions for the Raven's Standard Progressive Matrices over time documented by the psychologist James Flynn. Several psychologists, including Flynn, discuss the implications of these findings, which have now been termed the "Flynn Effect." The authors explore various explanations: test wiseness, environmental complexity, cultural evolution, school effects, home influences, and nutrition. The second section of the book focuses on Black-White test score differentials on achievement tests over time, particularly the National Assessment of Educational Progress (NAEP). The results suggest that the gap between Blacks and Whites is narrowing. Finally, the book consists of four chapters on the "dysgenic hypothesis" that differential fertility among low IQ samples will have a negative impact on the IQ of the population. Although not explicitly stated, the book appears intended for academics who teach courses dealing with intelligence. Each of the chapters reviews the literature in an area or explicates particular datasets. An understanding of psychometrics and statistics is helpful in comprehending the chapters.

In order to appreciate the volume, one should believe that the gains in IQ reported are real rather than artifactual. This will be difficult for anyone with a basic understanding of psychometrics. Score distributions for normative samples across time can only be fruitfully compared if the characteristics of the normative samples are identical across time. In the case of the Raven's Standard Progressive Matrices test, scores are correlated with educational attainment, which has increased over time. In the case of Black-White achievement differences, the gap has narrowed from a 1.23 standard deviation unit advantage to a .84 standard deviation unit advantage for Whites. Because the National Assessment of Educational Progress is a criterion-referenced assessment device, the gap would be expected to narrow due to ceiling effects. Meta-analysts consider a difference of .84 standard deviation units to be a large difference between groups.

The discussion of dysgenic trends suggests that simply predicting IQs of children from IQs of parents is problematic at best. The complex interaction of genes and environment makes predictions speculative. It also reinforces the need for longitudinal studies of changes in intelligence across generations.

A general misunderstanding that the volume perpetuates is confusing "stability of IQ, the tendency for IQ results to be consistent for a group of individuals over time, with "immutability." The editor views IQ changes as a challenge to immutability. Psychometricians clearly appreciate that IQs can change for individuals but correlations are stable for groups of individuals from one testing to the next.

From my perspective, the most interesting chapters are Neisser's introduction, Flynn's discussion of his analysis into IQ gains, and Patricia Greenfield's chapter on the cultural evolution of IQ. Neisser succinctly introduces the volume, putting each chapter in context. Flynn introduces studies on the gains in IQ over time and concludes that the reported gains are probable due to increases in generational improvements in test-taking skills rather than actual intelligence gains. Greenfield shows how computer games such as Tetris are similar to cognitive tasks that appear on intelligence tests.

Since the intended audience is unclear, it's hard to make recommendations regarding this volume. I believe that selected chapters such as Greenfield's would be valuable for selected readings in university courses dealing with intelligence. Students writing papers on topics such as "Nutrition and Intelligence" would benefit from examining those particular chapters. Due to its superficial treatment of psychometric issues, I would not recommend this volume as a textbook for a course on intelligence. Any of Sternberg's volumes in the Advances in Human Intelligence series or editions of the Handbook of Human Intelligence would be far superior. Because the word "gifted" does not appear in the index, I doubt that The Rising Curve will be of great interest to those in gifted education. The book will find favor among IQ opponents. Unfortunately, the politically correct conclusions will mask the specious scientific base underlying them.

Reviewed by Michael C. Pyryt, Ph.D., an Associate Professor of Applied Psychology and Director of the Centre for Gifted Education at the University of Calgary.