Gender Diversity of Research Teams and Clinical Trial Enrollment.

Importance: Inequity in clinical trial enrollment, particularly the underenrollment of women, is an ongoing concern in biomedical sciences. The extent to which increasing gender diversity among research teams, particularly, study principal investigators, could address this inequity is unclear. Objective: To assess the association between principal investigator gender and the proportion of women participants in clinical trials. Design, Setting, and Participants: This cross-sectional analysis used clinical trials registered on ClinicalTrials.gov that started enrollment after January 1, 2007, and completed enrollment before September 1, 2021, to analyze how the proportion of women participants in clinical trials varied by principal investigator gender, accounting for the disease being studied and when a trial was conducted (analyses were performed in October 2024). In an analysis of mechanisms, this study assessed whether specific decisions by investigators that could influence enrollment of women (eg, selecting women as study staff or including pregnant patients) varied by principal investigator gender. Exposure: Principal investigator gender. Main Outcomes and Measures: Proportion of trial participants who are women. Results: Across 10 708 trials, 3151 (29.2%) had a woman principal investigator. After adjusting for potential confounders, mean enrollment of women in trials with a woman principal investigator was 54.1% (95% CI, 53.0%-55.1%) compared with 46.9% (95% CI, 46.3%-47.5%) for trials in which the principal investigator was a man (absolute adjusted difference, 7.3% [95% CI, 6.7%-7.9%]; P < .001). Secondary analyses found that trials with a woman principal investigator had a higher proportion of women staff and were less likely to exclude pregnant patients. Conclusions and Relevance: This cross-sectional study of a large sample of clinical trials found that those with a woman principal investigator enrolled a higher proportion of women participants, had a higher proportion of women study staff, and were less likely to exclude pregnant patients. These results suggest that inequity in clinical trial enrollment, particularly the underenrollment of women, is an ongoing concern in biomedical sciences.