US research could be ��vulnerable�� to a double whammy of fewer Americans wanting to do a PhD and the supply of overseas students being dampened by the country��s political turn inward since the election of Donald Trump, experts warned in response to comparative data on global recruitment.

Data from the Organisation for Economic Cooperation and Development analysed by ����VR��Ƶ suggest that the country is falling behind many other developed nations on new PhD numbers.

Although about 71,000 people gained a PhD in the US in 2017 �C more than double the number in any other developed country �C when this is scaled to population size, the number of doctoral graduates in the US falls below many other OECD member nations.

And when an estimate of how many of these were international students is applied, the US appears to have one of the lowest numbers of domestic PhD graduates in the group.

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The figures could sound a warning to the US about the future of its research base, especially in the light of the reported downturn in the number of international students attracted to the country.

Earlier this month, one leading expert on global higher education warned that US-China trade tensions could spill over into international PhD mobility, with the UK and Germany possible beneficiaries as Chinese PhD students sought other places to study.

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The data on PhD graduates come from an analysis of OECD statistics on doctoral education.

When the figures are scaled for population size and estimates on international student numbers are included, Germany and Slovakia lead the OECD for the number of domestic doctoral graduates, with about 280 PhDs per million people in 2017.

They are followed by South Korea, Denmark, Finland, the UK, Australia and Switzerland. The last has a relatively high number of domestic PhD graduates even after taking out international students, who account for more than half its overall total. If international students are included, then Switzerland has by far the most PhD graduates for its population.

The US still has one of the highest shares of its population educated to doctoral level �C about 2?per cent of 25- to 64-year-olds have a doctorate, according to the OECD �C but the recent data on graduations suggest that other countries could catch and surpass it in the future.

Hans de Wit, director of the Center for International ����VR��Ƶ at Boston College, said a number of high-income countries had come to rely on the international market to ��compensate�� for the lack of domestic students wanting to do a PhD because of other ��competitive�� employment options in the labour market.

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But in the US, this situation could be ��more vulnerable�� as the increasing dependence on overseas PhDs could be combining with an ��unwelcoming environment�� towards international students, he added.

Philip Altbach, founding director of the centre, added that ��for decades�� the US had relied on international PhD students who then stayed afterwards, ��making up for fewer Americans choosing to do PhDs��.

��As the US becomes less friendly to foreigners and tightens up visa and immigration rules, this population is likely to decline.��

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Professor Altbach added that a ��problematic academic labour market�� for postdocs, particularly in non-science fields, was also contributing to the shrinking numbers pursuing a PhD. US universities had, in addition, been ��slow to train PhDs for non-academic jobs�� and thereby to make doctorates more attractive.

Elsewhere, the data point to the continuing strong position of Germany and Switzerland for PhD numbers.

Alexander Hasgall, head of the European University Association��s Council for Doctoral Education, said this was partly a reflection of the ��long tradition�� of PhD graduates in Germany being able to find work outside academia.

But, he continued, Germany and Switzerland also had ��diverse�� funding streams for PhDs that included national funders, universities (who may employ them as staff) and industry. ��There is not only one form of funding�� as in some other countries, he said.

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It is a point backed up by the OECD��s recent Education at a Glance report, which says that the ��strong financial input�� of business into research in places such as Germany and South Korea ��indicates that doctoral graduates could benefit from a wider range of research career opportunities beyond academia��.

simon.baker@timeshighereducation.com