US vs. EU scienctific productivity

From a study in the BMJ:

The research productivity of the first 15 countries to join the EU, adjusted for population, was lower (76%) than that of the US—and even lower (66%) when the 10 newest EU countries were included in the analysis.

This is based just on number of papers, so a crappy paper in a crappy, put PubMed indexed, journal counts the same one in Nature, but I suspect the US would do even better if quality were included.

One interesting, but hard, extension of this research would be to see what percentage of papers published in the US have either first or senior authors who are not US-native, and for the first author group, what percentage are not US permanent residents or citizens. I suspect that a lot of US scientific output is by immigrants, either temporary or permanent, some form the EU, but other from Asia and elsewhere.