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Chairman, Department of Hygiene and Epidemiology, University of Ioannina School of Medicine, Ioannina, Greece; Collaborating Scientist, Biomedical Research Institute, Foundation for Research and Technology-Hellas, Ioannina, Greece; and Adjunct Professor of Medicine, Department of Medicine, Tufts University School of Medicine, Boston, Massachusetts, USA
1Correspondence: Department of Hygiene and Epidemiology, University of Ioannina School of Medicine, Ioannina 45110, Greece. E-mail: jioannid{at}cc.uoi.gr
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94% of the expected top scientists worldwide have not been able to materialize themselves due to various adverse conditions. Scientific deficit is only likely to help perpetuate these adverse conditions.—Ioannidis, J. P. A. Global estimates of high-level brain drain and deficit. FASEB J. 18, 936–939 (2004)
Key Words: citations • scientific impact • migration • research • development
BRAIN DRAIN, the international migration of scientists in search of better opportunities, has been a long-standing concern (1
2
3)
, but quantitative measurements thereof are uncommon (4
, 5)
and limited to specific countries or disciplines. We need to understand brain drain at a global level and estimate the extent to which scientists born in countries with low opportunities never realize their potential. The deficit and migration of the scientific work force can happen at all levels, from undergraduate students to top-level, internationally established scientists. Focusing on the top scientists would offer a view on the ultimate major impact of these phenomena, since these scientists are the ones eventually responsible for major scientific progress and innovation.
It is understandable that there can be varying views on how top scientists should be defined (4)
. One approach is based on the number of citations they have received in their scientific field. Highly cited scientists are researchers who have received the highest number of citations in the period 1981–1999 in each of 21 scientific fields defined by the Institute of Scientific Information (ISI) (6)
. Despite some debate on the limitations of citation analyses (7)
and the inability to find a perfect means for weighting research accomplishments, citations directly reflect the use of scientific information in published research. Thus, the number of citations is a useful surrogate of scientific impact. While inclusion of specific individual scientists may be more or less reflective of major scientific contributions, highly cited scientists as a group represent a reliable sample of largely top researchers with major impact in their fields selected from a total of 5 million names authoring scientific papers in journals catalogued by ISI in the period 1981–1999. For each of the 21 scientific fields, the selected highly cited scientists are invited to post a biography in the ISI web site. For scientists who did not list place of birth and current affiliation on the ISI web site, personal or institution-affiliated web pages where this information might be provided were searched.
Countries of birth and residence could be retrieved for 1523 highly cited scientists. Their distribution across diverse scientific fields is shown in Table 1
. For 486 (31.9%, 95% confidence interval [CI] 29.6–34.3%), country of birth differed from the country of current residence. The average proportion of foreign-born scientists theoretically may be affected by the relative representation of different scientific fields in the sample analyzed. Reassuringly, the proportion of foreign-born scientists is very similar when estimated based on the actual available data (31.9%), weighing each scientific field equally (33.2%) or weighing each scientific field with the number of individual names of scientists included in the ISI Web of Knowledge for that field (31.1%). Regardless of the analysis used, the conclusion is that a third of the top scientists worldwide have migrated away from their native country and currently reside elsewhere.
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Migration has been more prominent in some scientific fields than others. There was significant variability in the rate of foreign-born scientists across scientific fields (chi-square P<0.001, Fig. 1
A). The lowest rates were seen in general social sciences (18%), immunology (19%), and clinical medicine (21%). The highest rates were seen in mathematics (55%), computer science (51%), economics/business (50%), and physics (50%).
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Of the 486 migrating scientists, approximately three-quarters (358/486, 73.7%) had immigrated to the United States (U.S.). Among resident scientists, the proportion of foreign-born was highly different across developed countries (chi-square P<0.001, Fig. 1B
). Foreign-born scientists accounted for about a third of scientists resident in the U.S., and the proportion was similar in Australia, Switzerland, Israel, France, and Netherlands. Compared with the U.S., the proportion was significantly lower in the U.K. (24%) and Germany (19%) and significantly higher in Canada (64%). Foreign-born scientists were uncommon or absent in Japan, Italy, Sweden, Denmark, and the rest of the world. Not a single foreign-born highly cited scientist was found residing in any country not belonging to established market economies (8)
, except for Singapore.
There was great diversity in the rates of emigrating scientists among those born in each country (chi-square P<0.001, Fig. 2
). Only 2% of U.S.-born scientists (95% CI, 1–3%) had migrated to other countries. Approximately one in five scientists born in Japan, Sweden, Denmark, or France had moved elsewhere. The rate was one in three or higher in other developed countries and approached two-thirds for the U.K. (56%) and Canada (63%). At least six of seven scientists born in India, Taiwan, or People’s Republic of China had moved elsewhere. In countries without a sufficient critical mass of locally born highly cited scientists (fewer than 12 scientists), 125 of 146 highly cited scientists had migrated (86%, 95% CI, 80–91%). Among countries without a sufficient critical mass of locally born scientists, the emigration rate was very high even in countries with established market economies (77% [95% CI, 65–87%]) and reached 93% (95% CI, 85–97%) in other countries.
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One may claim that migration of scientists is both useful and unavoidable. There are definite advantages for scientists to pursue opportunities to spend time in other countries: exposure to other ways of examining questions and broadening their views of science. An ideal scientific community in the setting of globalization may exhibit high, balanced rates of immigration to and emigration from each country. In fact, the very low emigration rate of U.S.-born scientists to other countries may be as disturbing a sign as the high rates of immigration to the U.S. for scientists born in other countries.
Under conditions of equity at a global level, the number of native top scientists in each country should be proportional to the population. Using population quotas for each country for 1981 (the starting year for the count of citations) (9)
, the expected number of top scientists born in each country can be estimated using the U.S. as a reference standard; the ratio of the number of born over expected scientists can then be calculated for each country (Fig. 3
). Compared with the U.S., the ratio was found to be 0.75 or higher in only 8 other countries (Luxembourg, Israel, Switzerland, New Zealand, U.K., Australia, Denmark, and Sweden, with ratios ranging between 0.80 and 1.86). The ratio was 0.50–0.74 in 6 other countries, 0.25–0.49 in 8 countries, and 0.10–0.24 in 13 countries. Thus, except for only 35 countries, individuals with the potential to become top scientists born in the rest of the world had less than a 10% chance of realizing their potential as compared with the U.S. Among the most populated countries, the ratios were 0.019 in India, 0.018 in the countries comprising the former Soviet Union, 0.014 in Mexico, 0.012 in Vietnam, 0.005 in People’s Republic of China, 0.004 in Nigeria, 0.004 in Pakistan, 0.003 in Brazil, and 0 in Bangladesh and Indonesia.
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Using the U.S.-born scientists as reference, it is estimated that 89% of individuals with the potential to make an impact comparable to that of the highly cited scientists analyzed have not attained this level. Calculations using only the population aged 15–64 in 1980 (the population directly at risk for becoming highly cited during 1981–1999) yielded similar results (87% deficit). Results were similar to more complex population weighing methods using population age adjustments for 5 year intervals.
The deficit is even larger when one considers another prominent inequality, the difference between genders (10
, 11)
. Representation of women among the analyzed sample was only 4% in U.S.-born scientists and 3% elsewhere in the world, whereas it would have been expected to be slightly over 50%, proportional to the percentage of women in the general population. No female scientists born in Asia were included in the sample of highly cited scientists. Using the U.S.-born male scientists as reference, there is an estimated 94% deficit of individuals who have the potential of achieving high scientific impact worldwide.
These figures pertain to the past two decades and may even underestimate the current situation. Although gender inequality is likely to be decreasing in some developed countries (12)
, the populations of countries where potential top scientists are unlikely to materialize have doubled in the past 25 years. Moreover, it is likely that scientific growth is multiplicative and progress is accelerated exponentially when the mass of scientists increases. Adverse conditions that hinder the development of top scientists are very complex (13)
. A few fields that may require very expensive instrumentation (e.g., nuclear physics) or sophisticated measurement or imaging techniques that have high purchase, service and maintenance costs are unlikely to flourish in most countries, whereas in other countries their growth may be feasible only in restricted settings (e.g., the military) rather than in academically independent research programs. However, in most fields large budgets are not necessary to produce top science and top scientists. For most scientific fields, poor prioritization for research, lack of competitiveness, lack of meritocracy, academic and often widespread social corruption, nepotism, gerontocracy, lack of transparent review for allocation of whatever funds are available and for the occupation of positions of academic leadership, and inefficient administrative structures that stifle creativity may interact to create stagnant environments that are adverse to scientific growth in many countries worldwide (14
15
16)
. Moreover, societal or personal prejudice precludes gender equality in education, essential to future development of top female scientists, and increases pressure on women as they struggle to realize their scientific potential.
The specific contribution of each drawback toward the paucity of top scientists may vary across different countries and different microenvironments, but these drawbacks are usually highly inter-related and coexisting. Moreover, these drawbacks probably overlap with the very key reasons that lead specific countries and the globe as a whole to developmental stagnation. Brain drain and deficit may not only be a consequence but also a prime cause of this stagnation. Lack of basic scientific progress may run in parallel with the difficulty of translating research findings for practical benefit (17)
. Not only developing countries, but also developed countries that cannot generate a critical mass of top scientists eventually are drained almost completely of their remaining scientific potential. This creates a vicious circle, since countries that lose their scientists may face difficulties in catching up with the pace of worldwide development. Furthermore, immigrants and minorities may face difficulties for advancement even in the best scientific environments (18
, 19)
. The major deficit of scientists and the strong global inequalities in this regard need to be addressed seriously. Adoption of repatriation schemes by countries that have long suffered from brain drain and the provision of incentives from countries like the U.S. for foreign-born scientists to return to their home countries with proper funding and research support may be one step to alleviate the problem. However, success may be limited unless there is a generous willingness to raise the overall concept of scientific research to a prominent place among societal priorities worldwide.
Received for publication December 8, 2003. Accepted for publication February 12, 2004.
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  S. Dodani and R. E LaPorte Brain drain from developing countries: how can brain drain be converted into wisdom gain? J R Soc Med, November 1, 2005; 98(11): 487 - 491. [Abstract] [Full Text] [PDF]
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