For many people, intelligence is one of those concepts that seems to make sense and should be relatively easy to define, until you have to think too deeply about it. What exactly is it, anyway? Is it a good memory, a quick wit, a special ability in mathematical skills? Remember from your reading that Charles Spearman identified intelligence as a general thing, g, that consists of general enhanced abilities in reasoning, verbal abilities, and logic. Robert Sternberg said intelligence is comprised of three parts: practical, creative, and analytical intelligence. Howard Gardner identified eight distinct intelligences. Others still found things like emotional intelligence and creativity of critical importance.

Just as it is difficult to narrowly define IQ, it is also difficult to measure it. Through the process of standardization and decades of administering IQ tests, researchers have a decent understanding that IQ can be generally measured, and that it is relatively stable over time. Even this belief in the validity and reliability of IQ testing continues to be challenged, however.

In 2011, Angela Duckworth (who is well known for her studies on grit), headed up a team of researchers who conducted a meta-analysis of nearly fifty previous studies. These studies examined the effect of monetary incentives on IQ tests, with varying values of money offered. Some were offered small incentives of a few dollars or less, others given moderate sums, and some received larger rewards of $10 or more. Duckworth and her team wanted to know if these incentives would impact IQ scores. What do you think happened? Sure enough, the study found that incentives increased IQ scores by an average of 0.64 standard deviations, which is roughly a 10 point different on the IQ scale! The effect of motivation was even more dramatic with larger rewards, and also had a larger impact on those who first reported lower-than-average baseline IQ scores. The impact of the motivation was much smaller with those with above-average IQs and was not even measured on those with baseline IQs above 120. Duckwork and her colleagues essentially conclude that motivation, as well as other external factors such as employment, years of education, and academic achievement, all have an influence on IQ scores. She warns against jumping to extreme conclusions, however, because both motivation and intelligence are needed to perform well on an IQ test.^[1]

You can see that this field of research is ever-growing and evolving. Contemporary studies are examining the genetic components that correlate with high intelligence, and new studies will assuredly reveal more about where intelligence comes from and how it is best measured.