Sunday, July 15, 2012

Does IQ Translate into Job Performance?

Jonathan Leake, the Science Editor for the Sunday Times, reports today that “women appear to have won a decisive victory in the battle of the sexes. Psychologists have found female IQ scores have risen above men for the first time. The findings have been made by James Flynn, a world-renowned authority on IQ tests. ‘In the last 100 years the IQ scores of both men and women have risen but women’s have risen faster’ said Flynn. This is a consequence of modernity. The complexity of the modern world is making our brains adapt and raising our IQ.” But does IQ translate into performance?

Flynn gives one possible explanation as “women’s lives have become more demanding as they multitask between raising a family and doing a job. Another is that women have a slightly higher potential intelligence than men and are only now realising it”.

IQ scores are used as predictors of educational achievement, special needs, job performance and income. They are also used to study IQ distributions in populations and the correlations between IQ and other variables. The average IQ scores for many populations have been rising at an average rate of three points per decade since the early 20th century, a phenomenon called the Flynn effect. It is disputed whether these changes in scores reflect real changes in intellectual abilities.

Whether IQ tests are an accurate measure of intelligence is debated. It is difficult to define what constitutes intelligence; instead it may be the case that IQ represents a type of intelligence.

According to Frank Schmidt and John Hunter, "for hiring employees without previous experience in the job the most valid predictor of future performance is general mental ability." The validity of IQ as a predictor of job performance is above zero for all work studied to date, but varies with the type of job and across different studies, ranging from 0.2 to 0.6. The correlations were higher when the unreliability of measurement methods was controlled for. While IQ is more strongly correlated with reasoning and less so with motor function, IQ-test scores predict performance ratings in all occupations.

That said, for highly qualified activities (research, management) low IQ scores are more likely to be a barrier to adequate performance, whereas for minimally-skilled activities, athletic strength (manual strength, speed, stamina, and coordination) are more likely to influence performance. It is largely mediated through the quicker acquisition of job-relevant knowledge that IQ predicts job performance.

In establishing a causal direction to the link between IQ and work performance, longitudinal studies by Watkins and others suggest that IQ exerts a causal influence on future academic achievement, whereas academic achievement does not substantially influence future IQ scores. Treena Eileen Rohde and Lee Anne Thompson write that general cognitive ability but not specific ability scores predict academic achievement, with the exception that processing speed and spatial ability predict performance on the SAT math beyond the effect of general cognitive ability.

Eliza Byington and Will Felps highlight how, “over the past century, numerous studies have documented the link between cognitive assessment scores and employee performance (see Schmidt & Hunter, 1992, 1998, 2004 for overviews). The strength of these findings has made intelligence “the most important trait or construct in all of psychology, and the most ‘successful’ trait in applied psychology” (Schmidt &Hunter, 1986). Few areas of scholarship produce such unequivocal findings and prescriptions for managers. In a chapter advocating the principle that employers should “select on intelligence,”Schmidt and Hunter state: “Intelligence is the major determinant of job performance, and therefore hiring people based on intelligence leads to marked improvements in job performance –improvements that have high economic value to the firm” (2000: 3). The assertion that intelligence leads to job performance is echoed in the titles of recent articles in which management researchers describe their findings: “Intelligence is the best predictor of job performance” (Ree & Earles, 1992), “The role of general cognitive ability and job performance: Why there cannot be a debate” (Schmidt, 2002), and “Predicting job performance: Not much more than g” (Ree, Earles, & Teachout, 1994). Building on this empirical foundation, researchers have gone so far as to provide methods by which managers and HR professionals can calculate the positive economic value of employing IQ-based selection in their organizations (e.g. Rauschenberger & Schmidt, 1987; Schmidt, Hunter, McKenzie, & Muldrow, 1979; Hunter &Schmidt, 1996; Schmidt & Hunter 1998).  

The industrial psychology literature has also reached a consensus on the explanation for the strong IQ – job performance relationship; namely, that individuals who are more intelligent (as measured by IQ scores) can learn job relevant knowledge faster and better, resulting in improved job performance (e.g. Ree, Carretta, & Teachout, 1995;Hunter, 1986)” (p.176).

However Byington and Felps weren’t totally convinced that the relationship between IQ and performance was a simple as past research had made it, stating “we suggest that the relationship between IQ and job performance is strongest in contexts where institutional architects have already adopted this edict, and in so doing, helped create its validity” – a bit like a self-fulfilling prophecy.

Tomas Chamorro-Premuzic probably sums it up best when he mentions that “there is a clear discrepancy between the scientific research evidence and what laypeople, and even some professional practitioners (HR departments, managers, recruiters, etc.) tend to believe. Thus scientists concluded long time ago that IQ is the most powerful psychological predictor of job performance, whereas laypeople tend to think of IQ as something that is useful only when it comes to predicting how well you do in a maths or general knowledge quiz - indeed, people with extremely high IQs are almost always portrayed as being geeky, weird and socially inept (an urban legend that has made Goleman, Gardner, and Sternberg rich and famous)”.


Byington, E and Felps, W. (2010). Why do IQ scores predict job performance? An alternative, sociological explanation. Research in Organizational Behavior, Vol. 30, p.175-202.

Chamorro-Premuzic, T. (2011). How Many Successful Entrepreneurs Would Fail an IQ Test? Psychology Today.

Leake, J. (2012). Women really are cleverer. The Sunday Times, 15th July, p.1.

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