Employers often rely on self-promotion to make decisions about hiring, promoting and offering raises to their employees, and self-evaluations are not only an inevitable part of measuring performance at our jobs, but a perfect opportunity to self-promote.

However, when it comes to talking ourselves up, women just aren’t as good at it as men.

The Harvard Business Review last week released data from a study that found a large gender gap in self-promotion — when asked, men rated their performance 33% higher than equally performing women.

To conduct the research, HBR looked at two factors that might influence one’s ability to self-promote: confidence and strategic incentives, such as a raise or promotion. To do the study, HBR recruited 1,500 workers from labor-market platform Amazon Mechanical Turk. Each person was asked four subjective questions they might be asked on a performance review.

Once the study was complete, researchers found men were substantially better at self-promoting than women even when they thought their answers would be communicated to employers who, in turn, would offer them incentives such as better pay or a promotion.

To see if the gender gap would persist, researchers also administered a private test to participants. What they found was even when no incentive was offered, women continued to rate their performance lower than men.

What drove this persistent gap? Researchers can only speculate, including that women are possibly internalizing the risks of describing their performance too favorably by fearing punishment for self-promoting “too much.”

Meanwhile, according to researchers, employers who base incentive on self-promotion should keep in mind that while women may not talk about their work as favorably as men, it doesn’t mean their performance is any worse.