NATURE BIOTECHNOLOGY VOLUME 24 NUMBER 7 JULY 2006 865

Research policy and the mobility of USstem cell scientistsAaron D Levine

State and national research policies governing human embryonic stem cell science are affecting the career plans of scientists in this exciting but controversial field.

Human embryonic stem (hES) cell research, because of the controversy it generates, is

governed by an unusually diverse and continu-ally evolving set of policies1. The uncertainty caused by this “regulatory patchwork”2 poses challenges for scientists entering the field and, anecdotally, has been credited with a significant impact on the geographic distribution of hES cell research. In the United States, research advo-cates worry that the nearly five-year-old federal funding restrictions are driving scientists abroad in pursuit of more favorable research climates and forcing researchers who remain home to focus on less controversial (and perhaps less promising) fields. State policymakers fear a “stem cell gold rush” in which top scientists pack their bags and head for California3, despite delays in the availability of funding promised by Proposition 71.

These worries are not irrational. Media reports and press releases have documented well-known stem cell scientists switching research institutes and countries. Postdoctoral researchers and other junior scientists have, no doubt, moved as well without generating the same fanfare. But job mobility is not limited to stem cell scientists. Scientists in all fields switch institutions and countries, yet these moves rarely attract media attention. Because of this disparity, it is hard to know if stem cell scientists exhibit more mobil-ity than scientists in less contentious fields.

Beyond these anecdotal reports, little is known about stem cell scientist mobility, a situ-ation that may be contributing to the continuing

Aaron D. Levine is in the Program in Science, Technology & Environmental Policy at the Woodrow Wilson School of Public and International Affairs, Princeton University, Princeton, New Jersey 08544, USA.e-mail: adlevine@princeton.edu

Table 1 Stem cell PIs in the United States received more job offers than PIs in otherbiomedical fields.

Percent of scientists Estimated difference

Stem cell Other Absolute Relative

At least one job offer 47.6 29.3 0.143 ± 0.043** 1.5×

At least one international job offer 14.9 2.8 0.068 ± 0.023*** 5.3×

Both US and international offers 12.0 1.6 0.057 ± 0.019*** 8.3×

Estimated differences are from the multivariate probit regression analysis, controlling for differences between the two groups of scientists. Absolute difference is the estimate (± s.e.m.) of the increase in probability of a stem cell scientist reporting receiving the specified offers. ***, P < 0.0001, **, P < 0.001, using two-tailed t-tests.

n = 1,019

deadlock over hES cell research policy in the United States. Indeed, Representative Chris Smith (R-NJ) recently stated that “there is no statistical evidence that scientists are leaving the country due to the current policy,” when argu-ing against increased federal funding for hES cell research4. Additionally, despite passage by the House of Representatives, Senate leadership has repeatedly delayed consideration of a bill that would relax federal funding restrictions on hES cell research5.

This article presents results from two surveys (see Supplementary Data online) designed to systematically assess if these reports of reloca-tion by stem cell scientists indicate a true policy impact or merely represent a distortion caused by atypical media interest. The data indicate that US stem cell scientists were significantly more likely than biomedical scientists working in less contentious fields to have received job offers to move to new positions in the 12 months pre-ceding the survey. This difference was particu-larly pronounced for international positions, suggesting US stem cell scientists are dispro-portionately considering leaving the country. Job offers received by stem cell scientists were skewed toward countries and states with permis-sive stem cell research policies.

Increased mobility for stem cell scientistsThe first survey specifically targeted US stem cell scientists and asked about career plans and the impact of policy on these plans. The second survey asked similar questions of molecular biologists, biochemists and physiologists in the United States who indicated they did not study stem cells. A total of 378 and 1,029 usable responses were received from the two surveys, respectively. Both surveys asked scientists whether or not they had received any job offers in the last year to move to a new position in their field. Because recruitment is often informal, job offers were defined broadly to encompass both formal written offers and serious discussions about potential moves.

The survey results indicated that among the subset of respondents who were principal investigators (PIs), mobility, as measured by job offers received, was substantially higher for stem cell scientists than it was for biomedical scientists in other fields (see Table 1). Indeed, stem cell PIs were 1.6 times more likely than PIs in the other biomedical fields to receive at least one job offer, 5.3 times more likely to receive at least one international offer and 7.5 times more likely to receive at least one inter-national and one domestic offer. Members of

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this latter group, estimated at 12% of stem cell PIs in the US, are presumably weighing the pros and cons of leaving the country to pursue their research.

These data suggest the excitement generated by stem cell research and the disparities created by the policy patchwork governing the field may indeed be increasing scientist mobility. To assess if these differences could be attributed specifi-cally to stem cell science, two analytic techniques (see Supplementary Data) were used to control for differences in potential confounding vari-ables, including age, gender, tenure status, coun-try of birth and the location of undergraduate and graduate education, between the two groups of scientists (see Supplementary Data online). Both techniques, multivariate probit regression (see Table 1 and Supplementary Data) and matching (see Supplementary Data), yielded similar results. Although the absolute differ-ences between stem cell scientists and other biomedical researchers were smaller once these variables were included, the differences remained significant. After controlling for age and other potential confounding variables with the regression framework, stem cell PIs were 1.5 times more likely to have received any job offer, 5.3 times more likely to have received at least one international offer and 8.3 times more likely to have received at least one domestic and one international offer than were the other PIs. The regression coefficient distinguishing stem cell PIs from PIs in other biomedical fields was significant in all three cases (≥1 offer, P = 0.0005; ≥1 international offer, P = 0.000004; ≥1 domes-tic and ≥1 international offer, P = 0.0000002; using two-tailed t-tests, n = 1,019).

A supportive environmentScientists who reported receiving job offers were asked about the states or countries in which the potential positions were located. Although many international positions reported by stem cell scientists were in countries with permissive research policies, too few international offers were reported to draw firm conclusions about their distribution. Clear, statistically significant differences were visible in the distribution of domestic job offers. In particular, nearly 34% of the job offers reported by stem cell scientists of all levels were for positions in California. In contrast, 11% of the offers reported by the other biomedical researchers were for positions in California. The state received 15% of the US National Institutes of Health’s grant funding in fiscal year 2004 (ref. 6).

Stem cell scientists also reported receiving disproportionately more job offers for positions in Massachusetts and New Jersey, both states that have passed legislation supporting research in the field. The absolute difference between the

percent of offers reported by stem cell scientists and by the other biomedical researchers were statistically significant for these states (CA, P = 7.2e-14; MA, P = 0.03; NJ, P = 0.003; using two-tailed t-tests, n = 787). These results (see Fig. 1) illustrate the impact of a supportive state environment and provide evidence that the dif-ferences in mobility reported here are due, at least in part, to policy disparities rather than other factors distinguishing the fields, such as the relative newness of stem cell research.

Given current interest in the field, this quan-titative evidence of relatively high domestic and international mobility among stem cell scientists may not be a surprise. Regardless, it bodes well for countries, including the United Kingdom7 and Singapore8, and states, including California, New Jersey, Connecticut and Maryland, that are investing in the field and striving to recruit researchers. Particularly when combined with recent reports suggesting the US is lagging in the production of hES cell publications9,10, these results lend credence to the claim that federal funding restrictions are negatively affecting the field’s development in the United States.

These results highlight the importance of public policy in shaping the field of stem cell research and hint at challenges facing policy-makers. State policy appears to be a potent tool for recruiting scientists, and permissive policies in some states may help the US retain scientists who would otherwise move abroad. However, as the challenges faced by the California Institute for Regenerative Medicine illustrate11, state policies pose difficulties of their own. They risk legal challenge and preemption by federal legislation, making stem cell legislation a risky gamble for individual states12.

ConclusionsJob offers provide a useful indicator of mobility but should not be taken as a guarantee of scien-tists’ plans. Not all of the scientists who reported receiving offers will move. Furthermore, many offers may be contingent on external events. California provides a case in point. The data presented here indicate that many stem cell

scientists are considering moves to California, and suggest that resolution of the ongoing liti-gation blocking distribution of the Proposition 71 funding may trigger significant migration to the state.

Although this survey addressed stem cell research as a whole, hES cell research continues to generate the most political attention. These data should help federal policymakers as they grapple with the potential benefits and costs of changes to the federal funding policy. The increased mobility seen among US stem cell sci-entists in the novel data reported here illustrate one potential consequence of leaving the status quo unchanged.

Note: Supplementary information is available on the Nature Biotechnology website.

ACKNOWLEDGMENTSThe author acknowledges the financial support of the Policy Research Institute for the Region at Princeton University, the National Science Foundation (through a Graduate Research Fellowship) and Princeton University. He thanks Lee Silver and Harold Shapiro for comments on an earlier version of the manuscript, Ed Freeland and James Chu for assistance on the design and implementation of the survey, Jesse Rothstein and Gerard van den Berg for assistance with the statistical analysis, Pete Farnham, Martin Frank and Nancy Witty. This project was approved by the Princeton University Institutional Review Panel for Human Subjects Research.

1. Walters, L. Kennedy Inst. of Ethics J. 14, 3–38 (2004).

2. Knowles, L.P. Nat. Biotechnol. 22, 157–163 (2004).3. Holden, C. Science 306, 1111 (2004).4. The Hill’s Congress Blog, 10 May 2006 <http://blog.

thehill.com/2006/05/10/the-truth-about-stem-cells>5. Weiss, R. The Washington Post, 24 May 2006, p. A12.6. US National Institutes of Health <http://grants.nih.gov/

grants/award/trends/states04.htm>7. Sample, I. The Guardian, 2 December 2005, p. 9.8. Normile, D. & Mann, C.C. Science 307, 660–664

(2005).9. Levine, A. Politics and the Life Sciences 23, 40–45

(2005).10. Owen-Smith, J. & McCormick, J. Nat. Biotechnol. 24,

391–392 (2006).11. Somers, T. The San Diego Union-Tribune, 10 December

2005, p. A1.12. Noll, R.G. in States and Stem Cells: Policy and Economic

Implications of State-Funded Stem Cell Research (ed. Levine, A.D.) 25–50 (Policy Research Institute for the Region at Princeton University, Princeton, New Jersey, 2006).

Figure 1 Stem cell scientists received proportionally more offers for positions in California and other states with permissive research policies. **, P < 0.01, *, P < 0.05, using two-tailed t-tests. n = 787 (292 offers to stem cell scientists, 495 to other biomedical scientists).

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