I have some question about the usage of the prepositions "among" and "in".
I have two contexts here. The first context concerns virus infection.
1a. The infection rate among elderly patients remains high.
1b. The infection rate in elderly patients remains high.
The second context concerns graduation rates:
2a. The graduation rate among recent immigrants remains low.
2b. The graduation rate in recent immigrants remains low.
Google searches suggest that, for the first context, both sentences 1a and 1b using prepositions "among" and "in" are standard English. But for the second context, Google searches suggest only sentence 2a using "among" is standard English. What do native speakers think?