The Study's Method of establishing if a student in the US educational Institution is actually from the US by Birth or a Naturalized US citizen after immigration is questionable as well as simply a citizen/national of some other country that's in the US for educational training.

Using English Language as the student's chosen best understood(Spoken/Written) language to determine if any student is likely from the US can result in students from other English speaking countries being included! And in the EU many can speak English/Other European language/Languages. So how to reduce any false positives there?