A recent study out of Sweden found that intelligence is correlated to higher earnings, but only up to a point.

Sweden has compulsory military service for males, and intake into the military includes a battery of psychological and cognitive tests. The researchers examined the IQ scores of the men when they were 18 or 19 and their wages between age 35 and 45. They found:

• Higher IQs were correlated to higher earnings, but only up to about $70,000, which was about the 90th percentile of earnings during the period examined.
• From the 90th to 95th percentile the relationship between IQ and earnings flattened (meaning that additional earnings didn’t correspond to increased IQ).
• From the 95th to 100th percentile IQ declined as compared with those in the 90-95th percentile, meaning that overall IQ declined as earnings increased. (Note that average IQs declined a bit — down to around the IQ of 90th percentile — not to moron status.)

What possible explanations are there for the plateauing and drop-off in IQ at higher income levels?

The study’s authors suggest two reasons: luck and family connections. Both of these reasons are a bit negative — they assume that the high earners, with their lower IQs, don’t deserve their high incomes. Sure, that happens and may explain some of the results. But does it happen enough to explain why IQ is lower for all the highest earners? Probably not.

Another possible reason suggested by other experts is that intelligence isn’t the only, or even the biggest driver, of career success. Emotional intelligence (EQ) is vital to career success and some studies have found that it is more important to success than IQ. And having a high IQ doesn’t ensure high EQ. In fact, sometimes, the smartest people lack high emotional intelligence. Think Dr. Sheldon Cooper on the TV show Big Bang Theory.

Thus, the Sweden study suggests that smarts only take you so far in your career. Something else — luck, family connections, or high EQ — is necessary to vault into the upper echelons of income earners.