If employers want to learn more about an employee’s personality, an award-winning study from the University of Iowa finds that the employee might not be the best person they talk to.

The study finds that personality traits are much more effective predictors of success if they’re rated not by the candidate but by someone who knows that person well.

“Observer ratings of personality traits have substantially higher validity in predicting overall performance compared with those based on self-reports,” says the study “Validity of Observer Ratings of the Five-Factor Model of Personality Traits: A Meta-Analysis,” co-authored by Michael Mount, professor of management and organizations in the Tippie College of Business, and two former doctoral students, In-Sue Oh and Gang Wang.

Employers and scholars have believed for years that personality plays an important role in explaining why people do what they do at work, but volumes of scholarly research have shown that personality traits are only moderately useful predictors of a person’s work success. The reason, Mount says, is that people are not always the best person to assess their own personality or capabilities. We all have a natural tendency to make ourselves look good, he says, and this is especially true in high-stakes situations like interviewing for jobs. It also could be that people are just not very self-aware.

Mount says the results of his study paint a much more optimistic picture of personality traits as predictors of job success. He and his co-authors looked at 15 earlier studies and found a common theme; personality tests are much better at predicting an individual’s performance if the assessments come from someone familiar with the employee such as a friend, co-worker, or some other acquaintance, someone who knows them well enough to analyze and assess their personality traits.

“We see ourselves quite differently than other people do,” says Mount, “And our results show that others’ perceptions of our personality predict job performance much better than our self-ratings."

In their analysis, the researchers found that the validity of assessments made by other people was twice as strong as self-reports in predicting employee performance.

Mount acknowledges that the use of ratings of personality traits made by others has its own challenges. The observers could have their own biases—the applicant or employee, for instance, isn’t going to give a prospective employer the name of someone who will say bad things about them—or not know enough about the person to give accurate answers. And as any supervisor who’s tried to get a reference knows, many employers refuse to provide anything but bare bones information about employees. He says getting around those limitations is a topic for future research.

The paper received the 2013 Hogan Award for Personality and Work Performance in April from the Society for Industrial & Organizational Psychology. The award is presented to papers that best demonstrate innovation in applied personality research. It was published in 2011 in the Journal of Applied Psychology.