Astronomers wanting time on the European Southern Observatory’s (ESO's) telescopes are less likely to get it if they’re women, an internal ESO study has found. Male-led proposals were selected 22.2% of the time, whereas female principal investigators won time only 16% of the time, according to the study, which was published on the preprint server arXiv this week. This discrepancy can be explained partly by the abundance of men at more senior career levels in astronomy, says study author Ferdinando Patat, an astronomer and head of ESO’s observing programs in Garching, Germany. Professional astronomers tended to be more successful in getting time than postdoctoral fellows and students, and men outnumbered women among the professional astronomer applicants by about four to one.

However, the review process cannot be cleared of unequal gender treatment, he says. When he accounted for the career level of the proposer, the gap in success rate shrank, but not completely: The success rate for men was 22.1%, comparable with the raw data, whereas women's success rate inched up to 19.3%.

Patat found other gender influences. When examining how the reviewers graded the proposals, he found that both male and female reviewers tended to rank proposals from female applicants more poorly, and the effect was worse for male reviewers. Female reviewers gave top ranks to 28% of proposals from women and 29.4% of proposals from men, whereas male reviewers handed out top ranks to 23.5% of proposals from women and 27.1% of proposals from men. The reviewers see proposals from all career levels, Patat points out, so there seems to be some gender-dependent influences in the review process.

The findings join the body of literature finding gender disparities in many aspects needed for a scientist’s career advancement, such as recommendation letters for postdoctoral fellowships. In 2014, a study on the proposal review process for the Hubble Space Telescope also found that proposals from men were more successful than those from women. This new study by ESO examined 13,420 proposals submitted by 3017 principal investigators from 2008 to 2016, and the 527 reviewers involved in grading proposals.

Although this study found that career level had the largest sway in the proposal review process, saying that gender bias doesn’t exist in astronomy would be false, says Meg Urry, an astrophysicist at Yale University. When you look at criteria used in science to hire people—for example, recommendation letters, number of citations, and teaching evaluations—all these metrics have been empirically found to be biased by gender, she says. “Women start with a deficit,” she says. “People like to talk as if the playing field is now level—and I think that’s partly because people wish it were—but the evidence shows otherwise.”

The fraction of female professors and the number of women in astronomy have grown, but there are still serious problems that need to be addressed, she points out. For example, the last couple of years have shown that sexual harassment was more common than many thought, she says. “Until we solve some of these problems, we shouldn’t pat ourselves on the back and say we’ve gotten there.”