The issue with the "american inventors" query is a well known issue in information retrieval called "compound intrusion." The phrase "american inventors" occurs

The issue with the "american inventors" query is a well known issue in information retrieval called "compound intrusion." The phrase "american inventors" occurs most often in web documents as a substring of "african american inventors" and unless you specifically exclude that from the results, it tends to dominate, producing the list of people you see there. If you search for "US inventors" you get a more reasonable list, because "US" isn't a substring of "african american."