Tag Archives: Daniel Willingham

After the Bell Curve: Research starts the conversation about IQ, again

13 May

Human Intelligence has a very good summary of the Bell Curve book:

The Bell Curve, published in 1994, was written by Richard Herrnstein and Charles Murray as a work designed to explain, using empirical statistical analysis, the variations in intelligence in American Society, raise some warnings regarding the consequences of this intelligence gap, and propose national social policy with the goal of mitigating the worst of the consequences attributed to this intelligence gap. Many of the assertions put forth and conclusions reached by the authors are very controversial, ranging from the relationships between low measured intelligence and anti-social behavior, to the observed relationship between low African-American test scores (compared to whites and Asians) and genetic factors in intelligence abilities. The book was released and received with a large public response. In the first several months of its release, 400,000 copies of the book were sold around the world. Several thousand reviews and commentaries have been written in the short time since the book’s publication….

The Bell Curve, in its introduction, begins with a brief description of the history of intelligence theory and recent developments in intelligence thought and testing, through the eyes of the authors. The introduction concludes with six important assumptions that the authors build much of the Bell Curve’s case upon. These six assumptions regarding the validity of “classical” cognitive testing techniques include:

There is such a difference as a general factor of cognitive ability on which human beings differ.

All standardized test of academic aptitude or achievement measure this general factor to some degree, but IQ tests expressly designed for that purpose measure it most accurately.

IQ scores match, to a first degree, whatever it is that people mean when they use the word intelligent, or smart in ordinary language.

IQ scores are stable, although not perfectly so, over much of a person’s life.

Properly administered IQ tests are not demonstrably biased against social, economic, ethnic, or racial groups.

Cognitive ability is substantially heritable, apparently no less than 40 percent and no more than 80 percent.

The authors proceed to explain, using classical cognitive test results primarily, to explain how lower levels of measured intelligence impact an individual’s, or indeed an entire class or group of individual’s life in American society. The rest of the book is divided into four major parts. http://www.indiana.edu/~intell/bellcurve.shtml

Needless to say, this book ignited a firestorm.

Cam Soucy has written an excellent summary of IQ tests for the Livestrong site in the article, What Is the Definition of IQ Test?


French psychologist Alfred Binet developed the the first IQ-style tests at the beginning of the 20th century. The first tests were designed only to assess the intelligence of children. The U.S. military relied on intelligence testing to assess and place recruits during World Wars I and II. Psychologist David Wechsler used the military IQ tests as a model in devising his own test in 1949. Today, a group of tests derived from Wechsler’s work are the most widely used IQ tests.

Download Free White Paper on assessment and teaching from CTB/McGraw-Hill CTB.com

The fourth version of the Wechsler Intelligence Scale for Children, the WISC-IV, was released in 2009. A companion test, the Wechsler Adult Intelligence Scale, targets people 16 and older. Other frequently used IQ tests include the Stanford-Binet Intelligence Scale, the Das-Naglieri Cognitive Assessment System and the Kaufman Assessment Battery for Children.


IQ tests commonly assess the taker’s logical reasoning, math ability, spatial-relations skills, short-term memory and problem-solving skills.


IQ tests originally were scored by dividing the subject’s “mental age,” as determined by which questions she answered correctly on the test, by her “chronological age,” her actual age in years, then multiplying that quotient by 100. For example, an 8-year-old child with a mental age of 12 would have an IQ of 125, with the calculation being 12/8 = 1.25, and 1.25 x 100 = 125. A person whose mental age precisely matched his actual age would have an IQ of 100, so a 100 IQ was defined as “average.”
Modern IQ tests no longer use such a formula. They simply compare a person’s test results with those of everyone else in the same age group, on a scale where 100 is defined as average intelligence.


Criticism of IQ tests focuses on the content of the tests–that is, the type of questions they ask–and their application. Such areas as vocabulary and “logic” can be strongly influenced by culture and socioeconomics. For example, consider a test that asks what word goes best with “cup”: saucer, plate or bowl. The test may intend “saucer” to be the correct answer. However, a test-taker who grew up in a home where tables weren’t set in a formal fashion might not know what a saucer is. He may be just as “intelligent” as the next person, but his score will suffer because of cultural factors. Authors of IQ tests are continually refining tests to address such concerns; some tests have removed verbal elements entirely.
Even test creators argue that the results are only one tool for assessing a person’s abilities, and that “intelligence” in a person is not a fixed quality, but changeable–even from day to day. In reality, however, people and institutions tend to put great weight on IQ scores. Students have been labeled “learning disabled” based on the outcome of IQ tests alone. As authors revise their tests, they also are revising their instructions to stress the tests’ limited application


Daniel Willingham, cognitive scientist and a psychology professor at the University of Virginia and author of “Why Don’t Students Like School?” His next book, “When Can You Trust The Experts? How to tell good science from bad in education,” will be published in July. He is written an interesting summary of his latest IQ study for the Washington Post.

In IQ: Willingham on the newest thinking, Willingham makes the following comments:

The American Psychological Association created a panel of eminent researchers to write a summary of what was known about intelligence, which would presumably contradict many of these claims. The panel published the article in 1996, a thoughtful rebuttal of many of the inaccurate claims in “The Bell Curve,” but also a very useful summary of what some of the best researchers in the field could agree on when it came to intelligence.

Now there’s an update. A group of eminent scientists thought the time was ripe to provide the field with another status-of-the-field statement. They argue that there have been three big changes in the 15 years since the last report:

(1) we know much more about the biology underlying intelligence; (2) we have a much better understanding of the impact of the environment on intelligence, and that impact is larger than was suspected; (3) we have a better understanding of how genes and the environment interact.

Some of the broad conclusions are listed below (note that these are close paraphrases of the article’s abstract).

The extent to which genes matter to intelligence varies by social class (genetic inheritance matters more if you’re wealthy, less if you’re poor).

Almost no genetic polymorphisms have been discovered that are consistently associated with variation of IQ in the normal range. “Crystallized” and “fluid” intelligence are different, both behaviorally and biologically.

The importance of the environment for IQ is established by the 12 to 18 point increase in IQ observed when children are adopted from working-class to middle-class homes. In most developed countries studied, gains on IQ tests have continued, and they are beginning in the developing world Sex differences in some aspects of intelligence are due partly to biological factors and partly to socialization factors. The IQ gap between blacks and whites in the United States has been reduced by 0.33 standard deviations in recent years.


Here is the citation and abstract of the work Willingham is commenting about:

Nisbett, R. E., Aronson, J., Blair, C., Dickens, W., Flynn, J., Halpern, D. F., & Turkheimer, E.

(2012, January 2). Intelligence: New Findings and Theoretical Developments. American Psychologist. Advance online publication. doi: 10.1037/a0026699


We review new findings and new theoretical developmentsin the field of intelligence. New findings include the following:

(a) Heritability of IQ varies significantly by social class. (b) Almost no genetic polymorphisms have been discovered that are consistently associated with variation in IQ in the normal range. (c) Much has been learned about the biological underpinnings of intelligence. (d) “Crystallized” and “fluid” IQ are quite different aspects of intelligence at both the behavioral and biological levels. (e) The importance of the environment for IQ is established by the 12-point to 18-point increase in IQ when children are adopted from working-class to middle-class homes. (f) Even when improvements in IQ produced by the most effective early childhood interventions fail to persist, there can be very marked effects on academic achievement and life outcomes. (g) In most developed countries studied,gains on IQ tests have continued, and they are beginning in the developing world. (h) Sex differences in aspects of intelligence are due partly to identifiable biological factors and partly to socialization factors. (i) The IQ gap between Blacks and Whites has been reduced by 0.33 SD in recent years. We report theorizing concerning (a) the relationship between working memory and intelligence, (b) the apparent contradiction between strong heritability effects on IQ and strong secular effects on IQ, (c) whether a general intelligence factor could arise from initially largely independent cognitive skills, (d) the relation between self-regulation and cognitive skills, and (e) the effects of stress on intelligence.

Here are some key findings of the study which deal directly with the Bell Curve:

Stress, Intelligence, and Social Class

One factor that Neisser and colleagues (1996) did not deal with extensively is stress. Chronic, continuous stress—what can be considered as “toxic” stress—is injurious over time to organ systems, including the brain. Chronically high levels of stress hormones damage specific areas of the brain—namely, the neural circuitry of PFC and hippocampus—that are important for regulating attention and for short-term memory, long-term memory, and working memory (McEwen, 2000). Although the extent to which the effect of early stress on brain development and stress physiology may affect the development of intelligence is not currently known, we do know that (a) stress is greater in low-income home environments (Evans, 2004) and (b) a low level of stress is important for self-regulation and early learning in school (Blair & Razza, 2007; Ferrer & McArdle, 2004; Ferrer et al., 2007). Research suggests that part of the Black–White IQ gap may be attributable to the fact that Blacks, on average, tend to live in more stressful environments than do Whites. This is particularly the case in urban environments, where Black children are exposed to multiple stressors. Sharkey (2010), for example, has recently found that Black children living in Chicago (ages 5–17) scored between 0.5 and 0.66 SD worse on tests (both the WISC-Revised and the Wide Range Achievement Test-3) in the aftermath of a homicide in their neighborhood. Sharkey’s data show that debilitating effects were evident among children regardless of whether they were witnesses to the homicide or had simply heard about it. An impressive study by Eccleston (2011) indicates that even stress on the pregnant mother may have enduring effects on her children. The children born to women in New York City who were in the first six months of pregnancy when 9/11 occurred had lower birth weights than children born before 9/11 or well after it, and the boys at the age of six were more than 7% more likely to be in special education and more than 15% more likely to be in kindergarten rather than first grade. Oddly, girls’ academic status was unaffected by mothers’ stress. Investigation of relations between early stress and intelligence thus seems an important direction for future research. A particularly important issue concerns the degree to which the effects of stress on the brain are reversible. These five unresolved issues are merely examples of some of the important contemporary paradoxes and unknowns in intelligence research. It is to be hoped that as much progress on these and other issues will be made in the next 15 years as has been made on some of the paradoxes and unknowns since the time of the Neisser et al. (1996) review.

IQ is not a simple concept and this newest research points to more questions than answers.

Dr. Wilda says this about that ©