In a recent post, I examined the NIH K99-R00 (Pathway to Independence) program. Looking at two cohorts of individuals who received K99 awards in FY2007 and FY2008, this analysis revealed that 91% of these 360 awardees transitioned from the K99 phase to the R00 phase, indicating that they had found suitable academic positions. Further, of those with such positions, 51% had obtained R01 funding through the present and some others had received other types of grants.
Over the process of organizing these data, I noticed that the fraction of women receiving K99 awards appeared to be lower than that for men. In order to examine this point more systematically, I assigned gender to these 360 awardees based on name and web searches. Overall, 142 of the 360 (or 39%) of the K99 awardees in these two cohorts are women. This is consistent with the value reported by NIH for this program.
Of the 218 men with K99 awards, 201 (or 92%) went on to activate the R00 portion. Of the 142 women, 127 (or 89%) went on to these R00 phase. These differences in these percentages are not statistically different.
Of the 201 men with R00 awards, 114 (57%) have gone on to receive at least 1 R01 award to date. In contrast, of the 127 women with R00 awards, only 53 (42%) have received an R01 award. This difference is jarring and is statistically significant (P value=0.009).
These results are summarized graphically below:
To investigate this further, I looked at the two cohorts separately. For the FY2007 cohort, 70 of the 108 men (65%) with R00 awards have received R01 grants whereas only 31 of the 62 women (50%) have (P value = 0.07). For the FY2008 cohort, 44 of the 93 men (47%) with R00 awards have received R01s whereas only 22 of the 65 women (34%) have (P value = 0.10). The lack of statistical significance is due to the smaller sample sizes for the cohorts separately rather than any difference in the trends for the separate cohorts, which are quite similar.
What could account for these disparities? Of course, it is unknown at this point if the differences reflect differences in R01 success rate as this would depend on the number of applications submitted by each applicant. I do not have access to data regarding the numbers of applications submitted by these grantees (although NIH does and could do this analysis).
One possibility is that the disparities is due to differences in the timing of funding for men versus women, that is, women might become R01 funded at more similar rates, but a greater disparity is observed at this point because of the lack of time for follow-up after the K99 award. To examine this point, I looked at the percentage of first R01 grants awarded each year to men and women as shown below:
The curves for men and women for each cohort are quite similar. This does not support the hypothesis that the timing of R01 funding is primarily responsible for the observed gender disparity.
Another factor that I considered is the impact of other R01-like awards, primarily the NIH Director's New Innovator (DP2) awards, on the analysis. Overall, nine K99-R00 awardees have received DP2 awards. Of these, six are men and three are women. Interestingly, three of these six men have subsequently received additional R01 awards whereas none of the three women have. In addition, one male K99 awardee received a Pioneer (DP1) award. The inclusion of these additional grants does not significantly affect the overall conclusion about the occurrence of a gender disparity.
Confirmation of and further analysis of these disparities is certainly warranted. Indeed, the K99-R00 program may be highly appropriate for such analyses as investigators at similar career stages competed for initial support and then obtained relatively comparable resources to launch their independent careers.