IQ isn't everything but it's a lot

A review of the latest research.

Written by Noah Carl.

In Part II of The Bell Curve, Richard Herrnstein and Charles Murray compared the effect of IQ on various outcomes (such as the probability of dropping out of high school and the probability of getting divorced) to that of parental socio-economic status. Across about a dozen total outcomes, they found that the effect of IQ was invariably stronger, often much stronger—leading them to conclude that “intelligence itself” is a major cause of social problems.

As you will know, the book came under tremendous assault after it was published, primarily because of the perfectly reasonable and heavily qualified comments the authors made about race and IQ. However, the book was also criticised for overstating the predictive value and practical importance of IQ. Detractors claimed that Herrnstein and Murray’s measure of parental SES was imperfect or even flawed, and that when confounding factors are properly controlled, the effect of IQ diminishes substantially.

The debate surrounding The Bell Curve raged in the mid-to-late 1990s. More than two decades later, where do things stand?

Even today, it is common to hear that the SAT (an IQ-type test used in college admissions) “favors rich, educated families” or that it is merely a “wealth test”. We are likewise told that “grit is more important than IQ when you're trying to become successful”. Scepticism about the practical importance of IQ is by no means confined to the popular media. A 2016 paper published in PNAS (a prestigious journal) and co-authored by James Heckman (a Nobel-prize winning economist) concluded that “personality is generally more predictive than IQ on a variety of important life outcomes”.

Can these claims be right? What does the latest research say about the practical importance of IQ—as compared to that of social background, personality and “non-cognitive skills” like grit?