Media Briefings


  • Published Date: December 2012

Any visa policies that restrict entry by highly productive foreign students are a significant barrier to science and ultimately to innovation and growth. That is one of the conclusions of research by Professors Eric Stuen, Mushfiq Mobarak and Keith Maskus, published in the December 2012 issue of the Economic Journal.

Their study of 700,000 postgraduates in the science and engineering laboratories of the top US universities finds that American students and foreign students are both highly significant contributors to the development of scientific knowledge. But greater diversity in the origins of foreign students raises their joint contribution to knowledge.

These findings imply that visa restrictions limiting the entry of high-ability foreign students – as well as visa policies that prioritise students’ ability to pay tuition fees over their technical merits – would significantly undermine scientific output.

The researchers note the current policy debate in both the United States and Europe about whether to relax limits on immigration by skilled scientists and engineers. Advocates argue that these skilled professionals contribute to innovation and are important for economic growth. Opponents fear they may displace similarly qualified domestic professionals.

This debate plays out most acutely over the issue of permitting foreign students to enrol in doctoral programmes in science and engineering and to remain in the country once they complete their degrees.

An important question is whether foreign students contribute to the knowledge base of the countries in which they study. They may do this most directly by participating in lab work in the science and engineering departments of research universities, which is the central focus of this study.

Using carefully structured statistical methods and a major database of all doctoral students at US universities, the researchers find clear evidence that both domestic and foreign students contribute strongly to the development of knowledge (as measured by publications and future citations).

In fact, the contributions of the two groups are comparable, with each student providing the talent and effort to support between four and five publications (and 180 citations) in each department over the time he or she engages in doctoral study and lab work. Indeed, university labs rely on the doctoral students they are training as an inexpensive source of skilled labour, which itself makes the labs more productive.

The fact that the contributions of foreign and domestic students to scientific output are similar is itself of great interest, for it suggests that university departments rationally choose between the groups at the margin to maximise research productivity.

But another important finding is that not all foreign students are alike: where visa restrictions limit the entry of highly productive students, the impact is to reduce publications and citations significantly, by close to 50%.

Finally, the researchers find that diversity in the origins of foreign students also contributes positively to knowledge creation: it is more productive for a department to have many countries represented than to admit students from just one country.

To reach these conclusions, the authors combine a database of around 700,000 doctoral students who graduated from doctoral programmes in 23 science and engineering fields at the largest 100 research universities from the 1970s to the 1990s, with data on scientific publications, macroeconomic conditions at the source countries that supply those students and source-country policies that restrict study abroad.

The most difficult task is to sort out the channels of influence – what social scientists call causality. If excellent students are attracted to doctoral programmes because those programmes have large amounts of faculty and research dollars, it may be the resources that really drive the publications. This makes it hard to identify the true contributions of the students themselves.

But students come from different countries and regions of the world, which go through large fluctuations in their own macroeconomic conditions and have their own policies about permitting citizens to undertake graduate study abroad. These factors generate exogenous shifts in the supply of such students, which can be used to analyse their impacts on publishing in US departments.

For example, the Asian crisis of the late 1990s and a series of decisions by China to permit foreign study had large effects on the enrolments of their students in specific scientific fields and universities. The authors use these episodes to identify such ‘shocks’ in enrolments and how they altered subsequent publishing.

To summarise, university officials who protest against visa restrictions that limit the ability of high-quality foreign students have a point, though perhaps not quite in the same way they envision.

Foreign and domestic doctoral students are both extremely important inputs into the production of basic knowledge, which must be acknowledged. In principle, tighter limits on foreign enrolments could be offset by enrolling more domestic students, but that would reduce research productivity (and raise costs) by relying on students of lesser ability.

Furthermore, any visa policies that restrict entry by highly productive foreign students are a significant barrier to science and ultimately to innovation.


Notes for editors: Skilled Immigration and Innovation: Evidence from Enrolment Fluctuations in US Doctoral Programmes by Eric Stuen, Mushfiq Mobarak and Keith Maskus is published in the December 2012 issue of the Economic Journal.

Eric Stuen is at the University of Idaho. Mushfiq Mobarak is at Yale University. Keith Maskus is at the University of Colorado.

For further information: contact Romesh Vaitilingam on +44-7768-661095 (email:; or Mushfiq Mobarak on +1-203-432-5787 (email:

Media Coverage

Times Higher Education The benefits of immigration on the lab: more papers and citations

New York Times Immigration and Innovation