Via Tyler Cowen, this is a genuinely startling result:
....material incentives in random-assignment studies increased IQ scores by an average of 0.64 SD, suggesting that test motivation can deviate substantially from maximal under low-stakes research conditions. The effect of incentives was moderated by IQ score: Incentives increased IQ scores by 0.96 SD among individuals with below-average IQs at baseline and by only 0.26 SD among individuals with above-average IQs at baseline.
Let me translate this into English. On IQ tests, a single standard deviation equals 15 points. So if this research is right, giving people actual incentives to do well on IQ tests (money, for example) has the following effect:
In other words, giving people an incentive to do well collapsed the gap between high and low by ten points — and bigger incentives created even bigger effects. These results are based on a meta-analysis of previous studies, not on new research, and metastudies are notoriously tricky to do properly. So take this with the usual grain of salt until these results get replicated elsewhere.
But ten points is a helluva lot. If this holds up, it's pretty significant.