Racial and Ethnic Diversity in Clinical Studies Reported to ClinicalTrials.gov, 2009-2024

ImportanceA lack of transparent reporting of race and ethnicity in clinical research limits the ability to identify health inequities and evaluate to what extent clinical research includes diverse populations. ObjectiveTo identify study characteristics associated with reporting race and ethnicity of clinical study participants and to document temporal trends in race and ethnicity reporting on clinicaltrials.gov. DesignCross-sectional analysis of interventional trials and observational studies from 2009-2024; multivariable logistic regression assessed study-level factors associated with reporting race and ethnicity. SettingGlobal registry of clinical studies (clinicaltrials.gov). Participants58,163 studies with posted results and without early termination. ExposuresStudy characteristics: sponsor trial phase, study type, and country. Main Outcomes and MeasuresReporting of race, reporting of ethnicity, reporting of both. ResultsAmong 58,163 studies (mean enrollment=1,215 participants), 44.8% did not report race or ethnicity to the repository (mean enrollment=1,481 participants). The proportion of studies reporting both race and ethnicity rose from 7.4% in 2013 to 54.6% in 2024. In multivariable models, observational studies had lower odds of reporting race and ethnicity (odds ratio[OR]=0.55, 95% confidence interval[CI]=0.49-0.61) compared with interventional trials. Phase 4 trials were least likely phase to report race and ethnicity (OR=0.32; CI=0.29-0.35), and studies with only National Institute of Health funding were more likely to report race and ethnicity compared to studies with any industry funding or sponsorship (OR=1.70, CI=1.61-1.79). For studies that reported race, White participants comprised [≥]50% each year based on study-level percentages; proportions of Asian participants declined, and Black participants fluctuated. Not Hispanic or Latino remained [≥]80% of reported ethnicity annually. Conclusions and RelevanceRace and ethnicity reporting on clinicaltrials.gov has improved markedly yet remains incomplete, with shortfalls in late-phase and observational studies. KEY POINTSO_ST_ABSQuestionC_ST_ABSAmong clinical studies registered to clinicaltrials.gov, how often are race and ethnicity reported, how has reporting changed across time, and what study characteristics indicate a higher likelihood of reporting? FindingsIn a cross-sectional analysis of 58,163 studies with posted results from 2009-2024 to clinicaltrials.gov, most studies did not report race and ethnicity, though rates rose from 7% to 55%. Reporting was less common in observational and late-stage clinical trials, and more common among NIH funded studies. MeaningDespite recent gains, incomplete reporting limits generalizable assessment of clinical study participant diversity and warrants stronger oversight.