Motivation and IQ: Incentives Matter
File this under "Smart Is Overrated."
…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.
via Motivation and IQ, incentives matter -- Marginal Revolution.