Psychology Textbooks Contain Inaccuracies on Intelligence

A majority of the bestsellers studied included misleading content.

Posted Mar 21, 2018

By Alexander Blum

In 1994, 52 professors involved in intelligence research and related fields signed a statement titled “Mainstream Science on Intelligence.” Following backlash against a controversial book, The Bell Curve, the statement attempted to correct misconceptions about the subject.

More than two decades later, a study suggests there are still some discrepancies between what many students are taught about intelligence and what scientists know about it. By examining how intelligence is portrayed in undergraduate psychology textbooks—and cross-referencing them with the 1994 statement, drafted by psychologist Linda Gottfredson, and the 1996 Neisser summary of intelligence research—the study’s authors unearthed assertions and characterizations that contradict mainstream research about intelligence and its measurement.

“This has been a major problem in intelligence research,” says Richard Haier, a Professor Emeritus of Pediatric Neurology at the University of California, Irvine and one of the signatories of the Gottfredson statement. “These textbooks just do not give a fair representation of what the data have been showing for the last 30 years.”

IQ is a measure of general intelligence, which according to the Gottfredson statement, “involves the ability to reason, plan, solve problems, think abstractly, comprehend complex ideas, learn quickly and learn from experience.” The statement also explains that IQ is related, “probably more so than any other single measurable human trait, to many important educational, occupational, economic, and social outcomes.”

Given that intelligence is genetically influenced and in turn predicts a wide range of outcomes, its measurement has long been a controversial subject. But in today's cognitively demanding economy, individuals with higher IQs may have more advantages than ever.

“Both (the Gottfredson and Neisser) statements hold up very well,” says Russell Warne, the Utah Valley University Associate Professor of Psychology and a co-author of the new study. “Experts in intelligence can quibble about some of the details, but generally, they’re a good foundation for anyone who needs an introduction to intelligence research.” Warne, along with colleague Jessica Hill and student Mayson Astle, ordered the 29 most popular introductory psychology textbooks assigned in American universities. All were published between 2011 and 2017. Combing through each textbook’s sections on human intelligence—which compromised 3.2 percent of the textbooks’ contents, on average—the researchers checked them against the information contained in the Gottfredson and Neisser documents.

By their count, 23 out of 29 textbooks contained “inaccurate statements” and 23 included “logical fallacies” in their content on intelligence. Some textbooks had just a few errors, others considerably more.

The most common types of inaccurate information, according to the researchers, included assertions that particular methods are known to be effective for boosting a person’s IQ, or that IQ is a subjective metric. One textbook claims: “...by selecting items for an intelligence test, a psychologist is saying in a direct way, 'This is what I mean by intelligence.' A test that measures memory, reasoning and verbal fluency offers a very different definition of intelligence than one that measures grip, shoe size, hunting skills, or the person’s best Candy Crush mobile game score.”

Undergraduates who read this might come away with a false sense that the concept of intelligence is based on arbitrarily chosen tasks, the researchers note. This may be especially likely for students who only take an introductory psychology course and do not major in the subject.

Despite these findings, Warne notes, the overall picture isn't so negative. “I think that the inaccuracies in introductory psychology textbooks are the result of honest error,” he says. “The fact that the average book only has 1.48 inaccurate statements in it means that most of what textbooks say about intelligence is accurate. That’s a testament to these authors’ sincere efforts to present a complex topic.”

Among the complexities explored by intelligence researchers is how much IQ can be changed. As the Gottfredson statement points out, “that IQ may be highly heritable does not mean that it is not affected by the environment.” But it also notes that IQ scores “gradually stabilize” in childhood. Understanding the extent to which they are susceptible to influence during the early stages of a person’s development, then, could be key to a future dialogue about intelligence.

“There might be 1,000 genes related to intelligence, each one having a tiny effect,” Haier says. “That’s a lot of genes to manipulate if you want to change intelligence. But it might be that a couple hundred of those genes affect one brain system in different ways, so you might target that brain system to influence intelligence.”

The prospect of increasing an individual’s IQ in this way, however, is still theoretical.

“There is a wide variety of evidence—especially from adoption studies—that a favorable environment does have a causal impact on individuals’ IQ scores,” says Warne. And in less developed nations, there is evidence that famine, lack of compulsory education, lead poisoning, and other early disadvantages can lower IQ scores. “But within typical environments found in industrialized countries, we don’t know much about how to raise IQ because the exact environmental components that raise intelligence test scores are currently a mystery.”

Warne remains “optimistic” about the potential to increase intelligence in the future, he says, “but also realistic. I don’t think that in the next 10 years we will have a pill to increase IQ in adults by 20 points. But we have made so much progress in raising IQ by increasing schooling and reducing lead poisoning, for example, that I think improvement is still possible.”

Alexander Blum is an Editorial Intern at Psychology Today.