Abstract
This Research Letter examines differences in the size of National Institutes of Health (NIH) grants awarded to first-time male and female principal investigators at top research institutions, including the Big Ten and Ivy League universities.
Federal funding is associated with the quality of science and researchers’ professional advancement.1 Female junior faculty received less university start-up support than males in one study,2 a factor associated with early-career attrition rates.3 We investigated another potential association: the size of National Institutes of Health (NIH) grant awards to first-time awardees.
Methods
Using the public NIH Principal Investigators (PI) database, we analyzed grant amounts to first-time female and male grant awardees from 2006 to 2017. A PI’s sex was determined algorithmically from first names. First-time PIs had no prior NIH awards as far back as 1985.
To examine factors related to funding, we first compared the median number of articles published per year, the median number of citations per article, and the number of areas of research expertise in published articles for first-time female and male PIs prior to their first NIH grant, using Microsoft Academic Graph (MAG). Areas of research expertise were estimated from the articles’ research topic as reported in MAG. Only articles with the PI as the last author were counted.4
To further control for confounding, we examined awardees of the top 10 most highly funded grants awarded to individual PIs only, which represents $14 billion in funding or 58% of all NIH funds awarded to 19 559 first-time PIs. Also, we investigated awardees at the same 14 Big Ten and 8 Ivy League universities ($1.8 billion in funding or 7.5% of NIH funds awarded to 8039 first-time PIs), as well as the top 50 NIH most highly funded institutions ($9 billion in funding or 38% of funding awarded to 20 335 first-time PIs). The 2-sided Mann-Whitney test of medians (threshold P < .05) and Python software (version 2.7.12) were used in the analyses.
Results
From 2006 to 2017, 53 903 NIH grants were awarded to first-time PIs across all 225 NIH grant types and 2766 institutions (Table 1). Of first-time PIs, 43.6% were female, similar to the female enrollment level of 38% in US MD-PhD programs during the same period.5
Table 1. Sex Differences in National Institutes of Health Grant Amounts to First-Time Principal Investigators (PIs) by Grant Type, 2006-2017.
| No. of Grants (% Female PIs) |
Total Funds, $ | Median Funds, $ | Median Difference (95% CI) | P Value | |||
|---|---|---|---|---|---|---|---|
| Male PIs | Female PIs | Male PIs | Female PIs | ||||
| All grant types | 53 903 (43.6) | 14 299 086 366 | 9 602 869 550 | 165 721 | 126 615 | −39 106 (−46 099 to −35 675) | <.001 |
| 10 Highest-funded grant typesa | |||||||
| N01 | 4294 (33.9) | 5 127 062 990 | 2 431 489 767 | 758 015 | 631 753 | −126 262 (−192 487 to −42 158) | .008 |
| U2G | 659 (40.2) | 620 904 033 | 403 834 797 | 635 700 | 706 812 | 71 112 (−48 258 to 245 451) | .21 |
| ZIA | 473 (36.1) | 251 977 313 | 161 597 279 | 593 777 | 541 648 | −52 128 (−201 599 to 135 016) | .44 |
| U01 | 1118 (40.9) | 502 103 617 | 293 859 180 | 442 335 | 350 000 | −92 335 (−138 305 to −24 242) | <.001 |
| U19 | 289 (29.7) | 99 530 085 | 38 978 847 | 287 250 | 260 842 | −26 408 (−94 772 to 64 675) | .74 |
| R21 | 4021 (39.1) | 514 696 219 | 329 828 103 | 210 673 | 211 477 | 804 (−3173 to 4558) | .45 |
| R01 | 6805 (35.1) | 1 714 019 703 | 966 030 337 | 348 596 | 364 509 | 15 913 (8625 to 22 803) | <.001 |
| P01 | 666 (27.6) | 153 880 046 | 56 634 953 | 234 354 | 224 150 | −10 204 (−50 026 to 18 305) | .07 |
| P50 | 519 (31.2) | 111 300 430 | 43 327 101 | 218 574 | 201 512 | −17 062 (−46 741 to 18 278) | .17 |
| P30 | 715 (34.7) | 130 140 753 | 46 459 974 | 150 333 | 149 473 | −860 (−22 017 to 17 127) | .69 |
| Total | 19 559 (35.7) | 9 225 615 189 | 4 772 040 338 | 316 350 | 305 823 | −10 527 (−17 240 to −3082) | .002 |
Excluded U54 grants, which are generally institutional and not individual awards.
Baseline performance measures were available for 73.4% of first-time PIs. No statistically significant differences by sex were found for baseline performance measures. The median number of articles published for men and women per year was 2.0 (P = .64), the median number of citations per article was 15 (P = .99), and the median number of research areas was 2.0 (P = .90).
For first-time PIs across all grant types and institutions, women received a median of $126 615 vs $165 721 for men (median difference, −$39 106 [95% CI, −$46 099 to −$35 675]; P < .001). For the 10 highest-funded grant types across all institutions, first-time female PIs received a median award amount of $305 823 vs $316 350 for male PIs (median difference, −$10 527 [95% CI, −$17 240 to −$3082]; P = .002), with the largest differences in N01 and U01 grants. However, women receiving R01 grants received $15 913 more than men (P < .001).
Female PIs at the Big Ten universities received a median of $66 365 vs $148 076 for male PIs (median difference, −$81 711 [95% CI, −$92 734 to −$67 450]; P < .001) (Table 2). Similarly, women at Ivy League universities received statistically significantly smaller grant amounts ($52 190 for women vs $71 703 for men; median difference, −$19 513 [95% CI, −$31 310 to −$6976]; P < .001). At the top 50 NIH-funded institutions, first-time female awardees received significantly smaller grant amounts ($93 916 for women vs $134 919 for men; median difference, −$41 003 [95% CI, −$47 052 to −$31 316]; P < .001).
Table 2. Sex Differences in National Institutes of Health Grant Amounts to First-Time Principal Investigators (PIs) by Institution, 2006-2017.
| No. of Grants (% Female PIs) |
Total Funds, $ | Median Funds, $ | Median Difference (95% CI) | P Value | |||
|---|---|---|---|---|---|---|---|
| Male PIs | Female PIs | Male PIs | Female PIs | ||||
| Big Ten University | |||||||
| Total | 4475 (43.2) | 759 569 110 | 339 745 391 | 148 076 | 66 365 | −81 711 (−92 734 to −67 450) | <.001 |
| Michigan | 910 (41.2) | 141 026 696 | 65 961 692 | 159 600 | 120 960 | −38 640 (−81 560 to −17 500) | <.001 |
| Northwestern | 611 (44.5) | 87 073 063 | 39 627 399 | 77 250 | 52 172 | −25 078 (−77 494 to −7259) | <.001 |
| Wisconsin | 569 (41.8) | 137 528 574 | 40 251 054 | 105 694 | 53 971 | −51 723 (−94 568 to −15 510) | <.001 |
| Minnesota | 566 (43.3) | 106 537 748 | 45 162 305 | 139 870 | 56 042 | −83 828 (−123 299 to −47 061) | <.001 |
| Ohio State | 342 (45.9) | 46 967 702 | 36 622 204 | 187 777 | 130 869 | −56 908 (−86 744 to −3736) | .03 |
| Iowa | 341 (40.2) | 63 480 034 | 22 356 759 | 160 013 | 97 200 | −62 908 (−130 710 to −24 651) | <.001 |
| Penn State | 298 (50) | 55 777 776 | 16 459 133 | 149 157 | 47 114 | −102 043 (−166 464 to −42 934) | <.001 |
| Illinois | 208 (42.3) | 21 983 400 | 13 978 567 | 64 171 | 48 255 | −15 916 (−38 387 to 1488) | .12 |
| Michigan State | 130 (50) | 19 983 899 | 19 990 339 | 163 290 | 76 750 | −86 540 (−148 787 to 76 019) | .32 |
| Maryland | 119 (47.1) | 12 952 641 | 5 375 086 | 152 000 | 47 408 | −104 592 (−178 234 to −20 000) | <.001 |
| Rutgers | 116 (40.5) | 33 708 247 | 7 697 544 | 249 000 | 77 083 | −171 917 (−247 750 to −47 350) | .004 |
| Purdue | 99 (39.4) | 13 633 152 | 6 630 927 | 173 286 | 149 827 | −23 459 (−94 849 to 34 916) | .34 |
| Indiana | 98 (38.8) | 12 001 025 | 6 782 321 | 172 681 | 92 458 | −80 223 (−174 882 to 92 180) | .57 |
| Nebraska | 68 (39.7) | 6 915 153 | 12 850 061 | 146 419 | 70 426 | −75 993 (−146 777 to 49 890) | .12 |
| Ivy League University | |||||||
| Total | 3564 (41.4) | 481 120 397 | 218 796 084 | 71 703 | 52 190 | −19 513 (−31 310 to −6976) | <.001 |
| Pennsylvania | 914 (42.8) | 114 250 899 | 46 932 468 | 78 681 | 52 154 | −26 527 (−53 526 to −7150) | <.001 |
| Harvard | 835 (39.2) | 92 162 114 | 44 437 929 | 53 318 | 47 606 | −5712 (−9856 to −2822) | <.001 |
| Yale | 697 (44.3) | 108 217 418 | 44 899 505 | 126 765 | 57 962 | −68 803 (−86 285 to −13 109) | <.001 |
| Cornell | 498 (39.6) | 65 519 644 | 36 179 905 | 49 646 | 52 190 | 2544 (−9112 to 13 588) | .75 |
| Brown | 203 (45.8) | 23 502 947 | 10 323 364 | 125 719 | 49 214 | −76 505 (−150 053 to −1127) | .004 |
| Dartmouth | 168 (39.9) | 34 470 140 | 10 509 570 | 141 750 | 123 909 | −17 841 (−87 065 to 50 130) | .17 |
| Princeton | 164 (37.2) | 20 509 968 | 15 466 356 | 52 190 | 53 541 | 1351 (−2904 to 5644) | .39 |
| Columbia | 85 (35.3) | 22 487 267 | 10 046 987 | 201 032 | 53 174 | −147 858 (−238 188 to 53 063) | .20 |
| All Top 50 Institutions | |||||||
| Total | 20 355 (43.7) | 5 243 541 876 | 3 891 624 358 | 134 919 | 93 916 | −41 003 (−47 052 to −31 316) | <.001 |
Discussion
This study found sex differences in the size of NIH funds awarded to comparable first-time female and male PIs, even at top research institutions. Funding disparities favoring men occurred among certain grant types, although for R01 grants, the most frequent award for first-time awardees, women received larger grants, as previously observed.6 Although the analyses controlled for key factors, limitations include possible unmeasured confounding and no data on grant applications that were turned down. Further study of the institutions where inequalities were lowest may provide insight into the reasons for sex imbalances in grant amounts awarded during formative career stages.
Section Editor: Jody W. Zylke, MD, Deputy Editor.
References
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