Being able to work well with others is a standard requirement for most jobs today. But a new study suggests that women do not get their fair share of credit for group work, especially when they work with men.

Heather Sarsons, a PhD candidate in economics at Harvard, gathered data on economists to see how teaming up with others (in this case to coauthor a paper) affects the likelihood of getting promoted (i.e., getting tenure), and whether it differs by gender. She found that coauthored papers correlate with fewer promotions for female academics. Women essentially experience a collaboration penalty, which is most pronounced when women coauthor with men and less pronounced the more female coauthors there are on a paper. Men, however, are not penalized at all for collaborating.

Women are tenured at far lower rates than men in academia, and prior research has found that this can’t be fully explained by differences in productivity or family commitments. Sarsons’s paper suggests another reason: the promotion gap appears when women work in groups with men.

“In economics, people often talk about it being dangerous for grad students to coauthor with professors because people assume the professor did all of the work. So I wondered from anecdotal stories whether women also received less credit for group work,” Sarsons told me. “We thought that bias might hurt people when it’s not really clear who did what on a project.”

Unlike papers in some other academic fields, where the order in which authors appear implies how much each person contributed, economics papers simply list multiple authors alphabetically by last name. So being the sole author of a paper sends a clear signal about your abilities, but being a coauthor sends a less clear one. Tenure committees then have to make a judgment call as to who put the most effort into the research — and this is where bias can creep in.

Sarsons looked at the CVs of 552 economists who went up for tenure between 1975 and 2014 in one of the top 30 PhD-granting universities in the United States. She coded where and when they received their PhD, their employment and publication history, their fields, and whether they received tenure. (Because the majority of schools require faculty to apply for tenure after seven years, she assumed that someone was denied tenure if they moved from a high-ranked university to a lower-ranked one after 6-8 years.)

Seventy percent of her full sample received tenure at the first school where they were eligible. However, only 52% of women received tenure, compared with 77% of men, despite there being no statistically significant difference in the number of papers that men and women produced or in how often they coauthored papers. She did find that men tend to publish in slightly better journals, but she said that this doesn’t explain the gap in tenure offers.

Women who solo-author all their papers have roughly the same chance of receiving tenure as a man; women who coauthor most of their work have a significantly lower probability of receiving tenure, even after controlling for things like productivity differences, school, year of tenure, field, and coauthor selection.

If you look at the chart below, you can see the relationship between tenure and the fraction of an economist’s papers that are solo-authored at the time he or she goes up for tenure. At the far left are economists who have coauthored everything and have no solo-authored papers. In this case, a woman has a 40% chance of receiving tenure, while a man has about a 75% chance. This gap shrinks as women solo-author more papers. Once they have only solo-authored papers, the probability for receiving tenure is basically the same for men and women.

Writing an additional paper is associated with a 5.7% increase in the probability of receiving tenure for both men and women, but a constant gender gap between promotion rates persists. Women are on average 18% less likely to receive tenure than a man, even after controlling for productivity differences.

Having an additional coauthored paper also increases the probability of getting tenure, but since it benefits men more than women (one coauthored paper has the same effect on tenure as a solo-authored paper for a man), the tenure gap grows the more coauthored papers they have.

The results also show that this coauthoring penalty for women is almost entirely driven from working with men. An additional coauthored paper with a man has no effect on a woman’s tenure, but when there is at least one other female coauthor on the paper, there is a small positive effect. And papers with only women are positively associated with tenure.

It’s tough to disentangle whether this coauthoring penalty results from employers not giving women as much credit when they work in a group with men or whether women are less likely to present or take credit for their work. There’s thinking that supports both of these scenarios: A 2005 study led by Madeline Heilman at NYU found that when men and women work together on a task — particularly a stereotypically male task involving leadership and decisiveness — outside observers (both male and female) devalue the women’s contribution relative to the men’s. And in 2013, another series of studies by Heilman and Michelle C. Haynes at the University of Massachusetts Lowell found that women gave more credit to male teammates for group work and took less credit themselves, unless their roles were irrefutably clear to outsiders. When they worked only with other women, this problem of not taking credit disappeared.

Sarsons presented a similar finding. She did a smaller study of sociologists to test her findings on economists and found that for sociologists, being first author on a paper is associated with a roughly 4% increase in tenure probability, regardless of gender. In sociology, being first author means you contributed the most, so there’s less uncertainty in terms of who did what, and women aren’t penalized for collaborating.

It’s important to note that these results are correlations; after all, there are other factors aside from papers that go into tenure decisions. Sarsons wasn’t able to account for things like teaching evaluations and letters of recommendation, for example. But her paper provides suggestive evidence that gender bias exists in academic promotion decisions, and that ambiguity about who contributed the most to a group paper tends to favor men unfairly.

This bias is a growing problem in economics since coauthored papers are becoming more common (perhaps due to larger-scale big-data projects that require more people). “My hope for this paper is not that women work in groups less,” Sarsons explained. “It is to bring attention to the fact that people might unconsciously be assigning credit for things differentially.”

We all want to believe that our work speaks for itself, but collaboration makes it inherently harder. As more and more jobs require group work, distributing credit fairly is becoming more challenging, even without gender bias in the picture. So it’s on employers to make sure that everyone gets the recognition they deserve, and it’s on employees to be adamant about claiming the credit they’re owed.