By Christian Jarrett

A researcher in human intelligence at Utah Valley University has analysed the 29 best-selling introductory psychology textbooks in the US – some written by among the most eminent psychologists alive – and concluded that they present a highly misleading view of the science of intelligence (see full list of books below).

Russell T Warne and his co-authors found that three-quarters of the books contain inaccuracies; that the books give disproportionate coverage to unsupported theories, such as Gardner’s “multiple intelligencies”; and nearly 80 per cent contain logical fallacies in their discussions of the topic.

Reporting their findings in an open-access article in Archives of Scientific Psychology, Warne and his colleagues say that altogether the widely used books contained “43 inaccurate statements, 129 questionably accurate statements and 51 logical fallacies” and therefore “members of the public [are] likely to learn some inaccurate information about intelligence in their psychology courses.”

In terms of topic coverage, over 93 per cent of the books covered Gardner’s multiple intelligences and over 89 per cent covered Sternberg’s triarchic theory of intelligence (both of which challenge the idea of there being a unitary “intelligence” per se), even though neither of these theories are mainstream or well-supported by evidence, according to Warne. In contrast, fewer than a quarter of the books covered the most strongly supported contemporary, hierarchical theories, such as Carroll’s three-statrum model and CHC theory each of which posits the influence of a general intelligence on other cognitive abilities.

To identify factual inaccuracies, Warne’s team used as a benchmark a consensus statement on intelligence research published in 1997 by Linda Gottfredson et al, and a 1996 APA report on the state of the field. Although no longer cutting edge, Warne chose these references because they reflect consensus in the field and because they are old enough for the information in them to have filtered through to non-specialist textbook authors.

The most common inaccuracy (appearing in nearly half the books) was that intelligence tests are biased against particular groups or individuals. This contradicts the 1997 consensus statement which tackles this issue and concludes that “intelligence tests are not culturally biased”.

Other common inaccuracies included promotion of the idea that it is not possible to measure intelligence in a meaningful way (in fact, Warne and his colleagues point out that “it is actually easier to measure intelligence than many other psychological constructs”), and claims that intelligence is only relevant in academic settings (in fact, intelligence correlates with many non-academic life outcomes, from life expectancy to risk of dying in a car accident, and is among the strongest predictors of career success).

Among the logical fallacies in the books is what’s known as “Lewontin’s fallacy” – this idea, advanced in six of the books, states that because humans share about 99 per cent of the same genes, that genes cannot therefore have a role in the differences between individuals or groups. In fact, “slight differences in genotypes among organisms can result in major phenotype differences”, according to Warne and his team. Twelve other fallacies appeared in the books – see full list above – such as giving less scrutiny to politically correct ideas or claiming that intelligence doesn’t exist because it is a collection of abilities (suggesting the textbook authors had failed to understand the principle of g or “general intelligence”).

In terms of questionable accuracy (i.e. errors not covered by the consensus statements), Warne highlights issues around the discussion of the taboo topic of race and IQ; textbook authors overplaying the role of “stereotype threat“, and authors having a tendency to overestimate environmental influences on intelligence (the books largely neglected the work of scholars who study the genetic influences on intelligence, such as the British researchers Ian Deary and Robert Plomin).

Warne and his team admit there is an element of subjectivity in their analysis of the textbooks. However, they tried to mitigate this by using the two consensus publications from the 1990s as a reference point, by being as lenient as possible in their judgments of the books, and by being explicit in the how they went about their analysis.

This new analysis helps explain why the public and lay journalists often express a scepticism toward intelligence and intelligence testing that is at odds with expert opinion (perhaps best captured by the hackneyed claim that “intelligence tests only measure your ability to take intelligence tests”). Over a million students take introductory psych courses every year in the USA alone (a majority of whom are taking the course as part of a different degree subject), and judging by the content of most popular introductory psych textbooks in America, it seems likely these students are getting a highly distorted view of the field.

An obvious issue for our domestic readers is that it’s not clear if the same inaccuracies and bias toward intelligence research also appear in British and European introductory textbooks. In fact this is a recurring shortcoming in our coverage of investigations into psychology textbooks – there simply doesn’t seem to be the same scrutiny of psychology textbooks here as there is in America.

“Improving the public’s understanding about intelligence starts in psychology’s own backyard with improving the content of undergraduate courses and textbooks,” Warne and his colleagues conclude. And for anyone who would like to know more about intelligence, they recommend Intelligence: All That Matters by Research Digest guest contributor Stuart Ritchie, and Intelligence: A Very Short Introduction by Ian Deary – these books are “not only accurate, but they also have a breezy writing style that makes them easily digestible”.

—What do undergraduates learn about human intelligence? An analysis of introductory psychology textbooks

Christian Jarrett (@Psych_Writer) is Editor of BPS Research Digest