NEW YORK: In workplaces that rely on peer-to-peer evaluation to award raises, bonuses or promotions, keeping introverted employees in good humour may help as they are biased against extroverted co-workers, a new research shows.

Shy employees are more likely to give poor evaluations of job performance with regard to their extroverted co-workers, the findings of two studies showed.

"We found that introverted employees are especially sensitive to their co-workers' interpersonal traits, in particular extraversion and disagreeableness," said co-author of both the studies Keith Leavitt, assistant professor at the Oregon State University in the U.S.

An extravert is high on sociability, talkativeness, energy and assertiveness.

Introverts consistently rated them as worse performers, and were less likely to give them credit for work performed or endorse them for advancement opportunities, according to the two studies.

"The magnitude with which introverts underrated performance of extroverts was surprising," Leavitt added.

"The results were very consistent across both studies," Leavitt said.

In one study, involving 178 MBA students, the researchers found 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 programme participated in a brief online game with three team mates.

The results showed that introverts gave lower evaluations and smaller peer bonuses to the extroverted team members.

Extroverted participants awarded evaluations and bonuses based on merit.

The findings appeared online in Academy of Management Journal.