The efficacy of IQ tests in predicting job performance is well established in the research. Linda Gottfredson, one of the leading researchers in the implications of general intelligence, g, (as measured by IQ tests) states: (Gottfredson, Linda S. “Why g Matters: The Complexity of Everyday Life.” 1997. Intellignce 24 (1) pp. 79-132.)
Personnel selection research provides much evidence that intelligence (g) is an important predictor of performance in training and on the job, especially in higher level work. … [In fact] g can be said to be the most powerful single predictor of overall job performance … no other single predictor measured to date (specific aptitude, personality, education, experience) seems to have such consistently high predictive validities for job performance.
On page 81 of that research paper, Gottfredson explains:
Research in job analysis and personnel selection refutes the claim that [general intelligence] g is useful only in academic pursuits. Intelligence turns out to be more important in predicting job performance than even personnel psychologists thought just two decades ago. And, very importantly, the research allows strong inferences about its causal importance.
Since World War II, the US military has recognized the importance of IQ in its recruitment policies. The extraordinarily high training costs and the high failure rates in the mobilization of low IQ military personnel in that War prompted the enactment of laws setting minimum enlistment standards. Currently the US Army using its AFQT tests require scores equivalent to an IQ greater than 85, while the Marine Corps and Air Force have a minimum standard equivalent to an IQ of 88 and the Navy, a minimum IQ of 91.
Of course, among those with approximately the same IQ there will be some variation in job performance; there are always examples of the “hare-and-the-tortoise” syndrome in which an individual of modest IQ has a strong work ethic and outperforms a brighter but less disciplined person, but these are the exceptions that tend to prove the rule.
At the high end of the IQ spectrum, we observe that the Nobel Prize winners, Fields Medallists, and top entrepreneurs in the Forbes list, all have high to extremely high IQ’s, combined with a very strong work ethic. As an old colleague of mine once observed, “There’s no substitute for brains.”
