Years ago, I told Tyler Cowen, "It's surprising that IQ tests predict life outcomes so well, because there's usually no financial incentive to get a high score." He replied, "People try out of pride - an under-rated motive." So when Tyler blogged Duckworth et al, "Role of Test Motivation in Intelligence Testing" I naturally took notice. Key claims:
1. Material incentives boost IQ scores: ... "The authors reasonably infer that IQ is more of a composite intelligence/motivation measure than usually believed - especially by inter-disciplinary researchers."
As far as I can tell, the authors do nothing to show that their results make IQ is less predictive. They don't even show that IQ is more mutable than earlier studies find; boosting incentives boosts scores while the incentives remain in place, but there's no reason to think the boost lasts after the test-takers receive their pay. All the researchers require us to reconsider is the reason why IQ is so predictive and hard to durably improve.
I made Duckworth's point in my 2007 FAQ on IQ:
Q. So, you're saying that IQ testing can tell us more about group differences than about individual differences?
A. If the sample sizes are big enough and all else is equal, a higher IQ group will virtually always outperform a lower IQ group on any behavioral metric....
Of course, everything else is seldom equal. A more conscientious group may well outperform a higher IQ group. On the other hand, conscientiousness, like many virtues, is positively correlated with IQ, so IQ tests work surprisingly well.
Q. Wait a minute, does that mean that maybe some of the predictive power of IQ comes not from intelligence itself, but from virtues associated with it like conscientiousness?
A. Most likely. But perhaps smarter people are more conscientious because they are more likely to foresee the bad consequences of slacking off. It's an interesting philosophical question, but, in a practical sense, so what? We have a test that can predict behavior. That's useful.