Yes, Smarts Matter.

“Just One More Thing…” is a short-form way that I share ideas, questions and guidance with more substance than a LinkedIn post and less academic rigor than my articles. I hope you find it valuable.

Intelligence

It’s hugely influential to success at work (and in life), yet few HR pros know its definition, where it matters most and how they should assess it.

What it is

A renowned intelligence researcher defined intelligence in her classic article, “Why g matters” as:

[Intelligence] . . . involves the ability to reason, plan, solve problems, think abstractly, comprehend complex ideas, learn quickly and learn from experience . . . it reflects a broader and deeper capability for comprehending our surroundings —“catching on,” “making sense” of things, or “figuring out”  what to do.¹

This means that more intelligent people more quickly and successfully do each of those things.

Intelligence has two related parts – fluid and crystallized. Fluid intelligence is one’s “processing power”²  – how quickly and effectively someone can do the things listed above. Crystallized intelligence is our storehouse of knowledge.³  People with higher fluid intelligence can fill that “crystallized” storehouse more quickly and use it more efficiently to make decisions, solve problems, etc.

Why it matters

Intelligence is the single largest predictor of performance at work and it’s twice as powerful as any other individual factor. Up to 40% of success at work in complex jobs is due to intelligence. More intelligent people typically move to higher levels at work. In fact, scientists can even identify the average IQ at different parts of the hierarchy:

Average IQ of Different Occupational and Educational Groups4

More complex jobs demand higher intelligence because they have a higher “cognitive load” or demand on your brain’s resources. Thus, there’s no job where more intelligence isn’t an advantage. This means the adage, “EQ is more important than IQ” is almost never true.

While higher intelligence is typically beneficial, your team may rate you as a worse leader if you have an IQ that’s too far above the team’s average. Research finds that a successful leader (as measured by their team members) has intelligence no more than 1.² standard deviations above the group mean – an I.Q. of around 120 if the group’s average IQ is 100 – 110.⁵

Intelligence is largely stable over time

One’s intelligence is significantly influenced by heredity and this influence grows over time. When entering the working world, about half of one’s intelligence is influenced by heredity, and its influence will increase throughout life to about 60%.⁶   Intelligence will change very little during one’s career.⁷  Individual efforts to improve one’s intelligence have not been shown to work over time^8,9.

Implications

It’s worthwhile to assess a candidate’s intelligence before you hire them for the reasons above. There are more and less precise ways to do that.

You want an indication of how intelligence can be applied at work, not just a raw measure of intelligence, so investigate tests like Watson-Glaser Critical Thinking Appraisal. This test is low cost, accurate and takes little time to complete.

You can invest more time and money using an assessment center or situational judgement tests. These can provide additional information about a candidate but are likely to also measure specific abilities and traits, not just cognitive horsepower.

Be extremely carefully using intelligence screens for existing employees. If you assess early-in-career employees, you may gain some insights about their future potential. But besides that, you should have sufficient insights from their performance history with your company or in previous roles to gauge whether they have the cognitive capability to move up.

Also, if you test an employee and they score low, are you really going to say, “Sorry, we just found out you aren’t smart enough to do the job”?

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Note: At the time this article was written (late 2024), there was a controversy among academics who study assessment techniques that predict job performance. While intelligence tests were long considered to be the most accurate way to predict job performance, some researchers now say that they have a large effect but not as large as previously stated.¹⁰

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References: 

1. Gottfredson, Linda S. “Why g matters: The complexity of everyday life.” Intelligence 24, no. 1 (1997): 79-132.
2. https://www.sciencedirect.com/topics/psychology/fluid-intelligence
3. https://www.sciencedirect.com/topics/neuroscience/fluid-and-crystallized-intelligence
4. Gottfredson, Linda S. “Why g matters: The complexity of everyday life.” Intelligence 24, no. 1 (1997): 79-132.
5. Antonakis, J., House, R. J., & Simonton, D. K. (2017). Can super smart leaders suffer from too much of a good thing? The curvilinear effect of intelligence on perceived leadership behavior. Journal of Applied Psychology, 102(7), 1003–1021. https://doi.org/10.1037/apl0000221
6. Plomin, Robert, and Ian J. Deary. “Genetics and intelligence differences: five special findings.” Molecular psychiatry 20, no. 1 (2015): 98-108.
7. Deary, Ian J. “The stability of intelligence from childhood to old age.” Current Directions in Psychological Science 23, no. 4 (2014): 239-245.
8. Buschkuehl, Martin, and Susanne M. Jaeggi. “Improving intelligence: A literature review.” Swiss medical weekly 140, no. 1920 (2010): 266-272.
9. Melby-Lervåg, Monica, Thomas S. Redick, and Charles Hulme. “Working memory training does not improve performance on measures of intelligence or other measures of “far transfer” evidence from a meta-analytic review.” Perspectives on Psychological Science 11, no. 4 (2016): 512-534.
10. See articles including the ones below for more information on the debate about predicting success at work. 

• Schmidt, Frank L., and John E. Hunter. “The validity and utility of selection methods in personnel psychology: Practical and theoretical implications of 85 years of research findings.” Psychological bulletin 124, no. 2 (1998): 262.
• Sackett, P. R., Zhang, C., Berry, C. M., & Lievens, F. (2022). Revisiting meta-analytic estimates of validity in personnel selection: Addressing systematic overcorrection for restriction of range. Journal of Applied Psychology, 107(11), 2040–2068. https://doi.org/10.1037/apl0000994 
• Oh, I.-S., Le, H., & Roth, P. L. (2023). Revisiting Sackett et al.’s (2022) rationale behind their recommendation against correcting for range restriction in concurrent validation studies. Journal of Applied Psychology, 108(8), 1300–1310. https://doi.org/10.1037/apl0001078 
• Sackett, P. R., Berry, C. M., Lievens, F., & Zhang, C. (2023). Correcting for range restriction in meta-analysis: A reply to Oh et al. (2023). Journal of Applied Psychology, 108(8), 1311–1315. https://doi.org/10.1037/apl0001116
• Kulikowski, K. (2023). “It takes more than meta-analysis to kill cognitive ability.” Industrial and Organizational Psychology 16, 366–370. https://doi.org/10.1017/iop.2023.36