  An imbalance in gender representation has been identified across many fields
of academic research. Men are disproportionately represented, especially at
senior career stages. Efforts to increase recruitment of women into training
programs has increased representation in many fields, but a "leaky pipeline" is
still observed: a disproportionate number of women leave research before
obtaining an independent position. To understand factors that lead to attrition
of women from academic research, we analyzed a database of mentoring
relationships covering the period 2000 to 2015 in several science and
humanities fields. While representation of women has increased over time among
both trainees and independent researchers, male graduate students and postdocs
still continue to independent research at higher rates than their women
colleagues. We analyzed aspects of the mentoring relationship that contribute
to this continuing bias. One strong pattern that is observed is homophily,
where trainees and mentors tend to be of the same gender. It has been
hypothesized that institutional bias may limit the influence of female
investigators, which could in turn impact the retention of their trainees in
academia. Indeed, we observe trainees of female mentors are less likely to
continue into independent research careers than trainees of male mentors. This
disparity persists, but is reduced, after controlling for temporal trends in
retention rates and under-representation of women mentors at the highest levels
of funding and citation. Although the trainee pool for mentors that receive
highly prestigious awards is skewed towards men, homophily is otherwise
unrelated to mentor achievement. These results suggest that, in addition to
other factors that limit career choices for female trainees, institutional bias
that gives female mentors access to fewer resources contributes to the leaky
pipeline for gender.
