There are obvious confounders. Medical journals are a small subset of journals and journals will have more academic representation, since that is the metric government panels use to give out grants, a concern private sector scientists don't have.
Writing in AEA Papers and Proceedings, they at least had one god reason for using medical journals for their analysis. In those, the last author listed on an article is the principal investigator who supported the work and has the highest level of prestige. So the researchers compared how many minorities and women were listed as last author on papers compared to white men. The software categorized author names by race, ethnicity and gender, which was another confounder. It also identified individual authors so that the researchers could follow how scientists' authorship position on papers changed over the course of their careers.
Overall, results showed that the probability of being a last author - the prestige position - increased from 18 percent during the first four years of a scientist's career to 37 percent after 25 and up to 29 years. Black scientists were substantially less likely to be last authors compared to white men after five years into their careers, with a gap of 6 percentage points at 25 to 29 years. The movement of women and Hispanics into last authorship was slower, with a gap of 10 percentage points after 25 years in their career.
It should have been worse.
Using statistical analysis, they say that blacks were 0.4 percentage points less likely than white men to be the last author and women were about 4 percentage points less likely to be listed last. Given that, it would have been reasonable to assume that the penalty for black women would be at least the sum of those two disadvantages, or 4.4 percentage points, but the findings showed black women were about 3.5 percentage points less likely than white men to receive the last authorship position.
Women of color lost something for being black and for being a woman, but less than simply adding those two disadvantages together. A similar result was found for Hispanic women.
The upside for the future is that academia has made real efforts to reward women and minorities. Handicapped people and Republicans are still being blocked out of tenure jobs, and universities don't have much interest in improving the lot for either of those groups.