Effort impacts IQ test scores in a minor way: A multi-study investigation with healthy adult volunteers

Test motivation has been suggested to strongly influence low-stakes intelligence scores, with for instance, a recent meta-analysis of monetary incentive effects suggesting an average 9.6 IQ point impact (d = 0.64). Effects of such magnitude would have important implications for the predictive validity of intelligence tests. We report six studies (N = 4208) investigating the association and potential causal link of effort on cognitive performance. In three tests of the association of motivation with cognitive test scores we find a positive, but modest linear association of scores with reported effort (N = 3007: r similar to 0.28). In three randomized control tests of the effects of monetary incentive on test scores (total N = 1201), incentive effects were statistically non-significant in each study, showed no dose dependency, and jointly indicated an effect one quarter the size previously estimated (d = 0.166). These results suggest that, in neurotypical adults, individual differences in test motivation have, on average, a negligible influence on intelligence test performance. (approximate to 2.5 IQ points). The association between test motivation and test performance likely partly reflects differences in ability, and subjective effort partly reflects outcome expectations.

Automated summary

Test motivation has a negligible influence on intelligence test performance in neurotypical adults, and individual differences in motivation may be attributed to differences in ability and outcome expectations.