All the “researchers” need to study is whether African-Americans change to “proper” grammar when talking to non-African-Americans. If that was true, what likely conclusions would “researchers” draw?
At one time I worked with a large group of blacks, one of whom was an educated black lady who was also a well known local public personality.
She was one of the most well spoken, clearest and precise speakers I have personally known.
In both public speaking and in personal conversations her delivery and use of the language was impressive.
One day I happened to walk in unnoticed on a group of blacks who were having a loud raucous group conversation.
They were speaking in what you might think of as black street idiom or gutter ebonics.
To me most of what I heard was barley understandable gibberish.
Imagine my surprise when I saw that one of the central speakers was the same lady who spoke such precise "white English".
She was holding forth in language that you would usually associate with uneducated black ghetto street people.
As time went by I learned that she and the other blacks could turn their "white" or "black" speech on and off like a faucet depending on the audience.