Introverted employees are more likely to give low evaluations of job performance to extroverted co-workers, giving introverts a powerful role in workplaces that rely on peer-to-peer evaluation tools for awarding raises, bonuses or promotions, new research shows.

Introverts consistently rated extroverted co-workers as worse performers, and were less likely to give them credit for work performed or endorse them for advancement opportunities, according to two studies from researchers at Oregon State University, the University of Florida and University of Notre Dame.

"The magnitude with which introverts underrated performance of extroverts was surprising," said Keith Leavitt, an assistant professor in OSU's College of Business and a co-author of the studies. "The results were very consistent across both studies."

The research offers new understanding of the role personality traits play in the workplace, where these days employees can have significant influence on their colleagues' careers, said Leavitt, an expert in organizational behavior. For example, at Google, colleagues can award bonuses to peers. And on the networking site LinkedIn, employees have the opportunity to recommend or endorse their peers.

"That gives employees a tremendous amount of power to influence their peers' career opportunities," Leavitt said. "It's something individuals and employers should be aware of."

The researchers' paper will appear in a forthcoming issue of Academy of Management Journal and is available online now. The lead author is Amir Erez of the University of Florida. Other co-authors include Pauline Schilpzand of Oregon State, Andrew H. Woolum of the University of Florida, and Timothy Judge of the University of Notre Dame.

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There is already considerable research that shows how an individual's personality traits might affect job performance, but there is little research that explores how one employee's personality traits might affect another employee in the workplace, Leavitt said.

That spurred Leavitt and his co-authors to explore how personality traits of one employee might affect that person's co-workers. They conducted two studies to test how co-workers' personalities interact to influence their evaluations of one another.

One study involved 178 MBA students at a large southeastern university. Each student was assigned to a four- or five-person project team for the semester and midway through the term, participants completed questionnaires about their team members, team processes and their own personalities.

The results showed that introverted team members rated the performance of other introverts higher than that of extroverts. In contrast, ratings made by extroverts were not significantly influenced by the personalities of the team members they were rating.

In the second study, 143 students in a management program participated in a brief online game, lasting about 10 minutes, with three teammates. Unbeknownst to the participants, the teammates were all electronic confederates, and one target team member's profiles and comments during the game were manipulated at random to highlight high introversion or extraversion, while their actual performance of the task was held constant.

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The participants then evaluated their team members and made recommendations about promoting or awarding bonuses to their teammates. The results showed that introverts gave lower evaluations and smaller peer bonuses to the extroverted version of the targeted team member, even though all the versions of the confederate team member performed the same. Extraverted participants were largely unaffected by the interpersonal traits of their team members and awarded evaluations and bonuses based on merit.

"We found that introverted employees are especially sensitive to their co-workers' interpersonal traits, in particular extraversion and disagreeableness," Leavitt said. "They make judgments and evaluate performance of others with those traits in mind."

Leavitt suggested that extraverted employees might need to use a "dimmer switch" when interacting with introverted peers, and employers or supervisors may need to consider that the personality traits of evaluators could bring a degree of bias into evaluations, bonus awards or other personnel decisions that rely on peer-to-peer feedback. Managers also may want to reconsider forcing interaction among employees or teams, he said.

In future studies, researchers hope to further explore how personality traits impact team effectiveness, including a closer examination of the line where personality issues affect team functionality, Leavitt said.

Introversion and extroversion are not the best overall predictors of job performance, either, he said. Conscientiousness has shown to be the best trait for indicating how an employee will actually perform.