For his study, published this week in Psychological Science, Grant tracked the sales of 340 people who worked for an outbound call center for a software company.
Over a three-month period, ambiverts achieved average revenues of $16,393. That was 24 percent higher than the results for introverts and 32 percent higher than for extroverts. The difference between extroverts and introverts was not statistically significant.
Grant, who is on tour to promote his book, Give and Take: A Revolutionary Approach to Success, said he was inspired by Susan Cain's book, Quiet: The Power of Introverts in a World That Can't Stop Talking.
Grant, 31, a prolific writer of journal articles, says he is "one of the more extroverted of the introverted." The book made him think about how people in the U.S. undervalue introverts, but also discount the downside of generally positive qualities. "Introverts have strengths and extroverts have weaknesses," he said.
According to Grant's study, one in nine Americans works in sales. Extroverts, he said, gravitate to sales jobs and are more likely to be hired for them. There's reason to think they will be good at them. They're more at ease initiating contact, express much enthusiasm, and are often more forceful than introverts.
But past work on extroverts' effectiveness has questioned the bias in their favor. Grant thought that adding ambiverts to the analysis would lead to a U-shaped success curve, and it did.
Grant thinks extroverts may spend too much time delivering their high-energy pitches and not enough listening to what their customers have to say.
Ambiverts may be more flexible and better able to "strike a balance between talking and listening, avoiding the risks that extroverts face of failing to understand customers' needs and appearing . . . pushy."
He said companies would do well to teach some of their highly extroverted sales people to behave more like their quieter peers. They might also want to downplay personality in job interviews and evaluate skills.
Most people, he wrote, are well suited to sales, but companies may not be making the best talent choices. "My findings suggest that less-extroverted people may be missing out on productive careers," he said, "and hiring managers may be missing out on star performers."
Contact Stacey Burling at 215-854-4944 or firstname.lastname@example.org.