Is there a gender-based promotion gap? Are there too many women who do well on the job, but are not considered seriously for career advancement?

Some new supporting evidence has come to light. A recent study using a database of almost 30,000 management-track employees at a large retail chain found that the women received higher job-performance ratings, but lower ratings for "potential.” Those same women were also promoted less, although they ended up performing better than their male counterparts. Perhaps most significantly, almost half of the promotion gap correlated with the lower ratings of "potential.”

Bias isn’t the only possible explanation. The study’s conclusions can be challenged on the basis of the size of the effect, or in its interpretation. The researchers calculated, for instance, that a woman’s chance of being promoted in a given year was between 1% and 2% less than the chance of a man being promoted. Is that a difference so small it might be random, or the result of measurement error? Or does it accumulate over time and put qualified women at a significant disadvantage?