Generally, Engle said, different IQ tests correlate well with each other and scores tend to be linked to real-world outcomes. Compared to people who score lower on the tests, for example, people with the highest IQs file more patents, publish more academic papers, and earn higher incomes.
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But scoring well on an IQ test doesn't predict success, nor does a relatively average or lower score predict a life of misery.
That's because having a high IQ is like owning a car with a big engine, said David Lubinksi, psychologist and co-director of the Study of Mathematically Precocious Youth at Vanderbilt University in Nashville, Tenn.
"If there's no gas in your car you're not going to go anywhere. If road conditions are bad, you're not going to go anywhere," he said. In the case of intelligence, you need good health, hard work and motivation to take advantage of inherent brainpower.
Another complication is that intelligence comes in many forms. One category is crystallized intelligence, Engle said, which measures how much knowledge a person has acquired and that is highly correlated to education level.