According to this study:
1. Doctors who graduated from foreign medical schools, and who were not US citizens when they went to medical school, who then went on to practice in the US, had significantly lower mortality rates
than a) doctors who went to US medical schools and b) doctors who went to foreign medical schools and who were US citizens when they went to medical school.
2. No significant difference in mortality rates
between a) all international medical graduates and b) graduates of US medical schools.