Another was told that both their tests and their self-evaluations would be provided to those employers.

Another was told that only their tests would be provided to the employers. And a "private" version did not involve hypothetical employers but instead involved providing their tests and self-evaluations to their fellow test-takers.

These changes sought to correct for possible propensities to inflate one's test performance to improve potential job and salary offers or to see whether self-promotion decreased in either sex if there was no benefit to be had by promoting oneself.

And while there was less self-promotion with no potential boss in the wings, the reduction was equal among sexes, thus preserving the gender gap.

The report says, "In every setting we explored, we observed a substantial gender gap in self-promotion: Women systematically provided less favorable assessments of their own past performance and potential future ability than equally performing men. And our various study versions revealed that this gender gap was not driven by confidence or by strategic incentives, and that it was robust both in the face of ambiguity and under increased transparency."

More research is necessary, the report concludes, to determine why women do so much less self-promotion than men.

But in the meantime, it warns, "employers relying on self-promotion to make hiring, promotion, salary, or bonus decisions should heed the lessons from this work: Women may not talk about their work as favorably as men, but that doesn't mean their performance is any worse."

READ MORE:

• Who's responsible for putting an end to the gender pay gap?
• Gender pay gap analyses becoming standard practice
• Retirement inequality on the rise