On January 27 President Trump signed an executive order blocking citizens, including doctors, from seven Muslim-majority countries from entering the U.S. for 90 days. This may have a measurable impact on the U.S. health care system. Many doctors may be blocked from returning to the U.S. after leaving the country. According to 2010 data, of approximately 850,000 doctors providing direct patient care in the U.S., 4,180 physicians were Iranian citizens and 3,412 physicians were Syrian citizens.

There are currently 260 people from the seven countries who are applying for residency slots in U.S. hospitals but are now banned from coming to the U.S. Match day, when students learn whether they have been accepted into a program, is on March 17, just over a month away. If the U.S. loses these applicants and cannot find candidates to take their spots, a simple calculation shows that this could affect 400,000 patients over the next year alone (estimated with assumptions that 50% of them successfully match to residency programs, become primary care doctors, and see 3,000 patients over the next year).

Approximately one in four practicing physicians in the U.S. completed medical school abroad. Many international medical graduates come to the U.S. for residency and then stay, agreeing to work in areas where there’s a shortage of health professionals. Studies have shown that internationally trained doctors are more likely to practice medicine in rural and underserved areas. In many instances, the doctors end up working in these areas for long periods of time.

Policy makers and the public have expressed concerns over the quality of work provided by immigrants, as compared to U.S.-trained doctors, despite the fact that internationally trained doctors have to pass three exams, complete residency in the U.S., and be licensed to practice in the U.S. While the issue has been debated for decades, there has been sparse evidence on whether patient outcomes differ based on where a physician went to medical school. Prior studies have produced mixed results, but they have usually examined small sample sizes or focused on narrow geographic areas.

In a recent paper published in The BMJ, we found that when Medicare patients were admitted to U.S. hospitals with general medical conditions, their probability of dying within 30 days of admission was 5% lower if they were treated by international medical graduates than if they were treated by U.S. medical graduates. We found no difference in whether patients were more likely to be readmitted to the hospital within 30 days after being discharged. We also saw that the cost of care was somewhat higher with foreign medical graduates than with U.S. medical graduates, though the difference was very small.

To arrive at these findings, we studied outcomes of Medicare patients treated by internationally trained internists and domestically trained ones. We measured across hospitals and within the same hospital to avoid hospital effects confounding our results. It is well-known that foreign medical graduates are more likely to practice in rural, underserved areas, where hospital resources may be lower and illness severity of the patient population may be higher. Both factors would lead to higher mortality among patients treated by foreign medical graduates, even if these physicians’ practice patterns and quality of care were identical to domestic medical graduates. So, by comparing patients treated by international versus domestic medical graduates within the same hospital, we effectively eliminated the effects of hospital quality and population characteristics on patient mortality. We also adjusted for several patient characteristics (e.g., age, gender, race, severity of illness, and socioeconomic status) and physician characteristics (age, gender, and how many Medicare patients they treated per year) to isolate the effects of medical school on patient outcomes.

We looked at care provided by more than 44,000 internists for over 1.2 million hospitalizations. In general, patients treated by international medical graduates were more likely to be a racial minority, have lower socioeconomic status, and have more comorbidities. After adjusting for patient, physician, and hospital factors, we found that patients treated by international medical graduates were less likely to die (11.2%) than patients treated by U.S. medical graduates (11.6%) in the 30 days following hospitalization. The difference was statistically significant, and we observed the same patterns when we compared physicians across hospitals or within the same hospital.

We also found that, 30 days following a hospitalization, patients treated by U.S. medical graduates and international ones (within the same hospital) were equally likely to have been readmitted to the hospital. Compared to U.S. medical graduates, international graduates spent slightly more on treating patients (e.g., through more tests and imaging studies), but the difference was very small ($47 per hospitalization). We also performed a number of sensitivity analyses to test whether our findings were affected by different assumptions that included how long patients stayed in the hospital, whether the patient was sent home or to a rehabilitation facility, and whether the hospital was a teaching hospital. Our findings were consistent across all analyses.

There are a number of possible explanations for why patients treated by international medical graduates are less likely to die. One reason is that in order to work as a physician in the U.S., international graduates must go through extraordinarily tough selection processes, which select the best of the best physicians from each country. For instance, only 49.4% of international medical graduates that apply end up with spots in U.S. residency programs. The tendency for international graduates to score higher on tests than U.S. graduates also supports this hypothesis. International graduates typically undergo more training — initially in their home country, and then again in the U.S. Yet we don’t know the degree to which any of these factors explains our results. Future work should explore exactly why international medical graduates deliver higher-quality care.

Our findings suggest that internationally trained doctors provide slightly higher quality of care than domestic medical graduates, at least in general treatment of Medicare patients. International graduates are vital to providing health care in the U.S., and policies that discourage doctors from other countries from wanting to practice in the U.S. are likely to have unintended consequences for the health of American people, especially for those who live in traditionally underserved areas.