A new study by scholars at Harvard finds that when employers evaluate several candidates for promotion simultaneously rather than individually, it can lead to fewer instances of gender discrimination. According to the study, this happens because comparing two candidates at the same time places greater importance on past performance, whereas any gender bias the empoyer may have can come to the fore in evaluating a single candidate. In addition, the study finds that simultaneous evaluations can result in better hiring decisions, and greater efficiency in the hiring process.
See "To Curb Discrimination, Compare Candidates Side-by-Side", Rachel Emman Silverman, The Wall Street Journal, January 8, 2013