I would suggest you read up on Simpson's paradox.[0] The study is not eliminating their performance just categorizing them. [0]: https://en.wikipedia.org/wiki/

I would suggest you read up on Simpson's paradox.[0] The study is not eliminating their performance just categorizing them. [0]: https://en.wikipedia.org/wiki/Simpson%27s_paradox https://en.wikipedia.org/wiki/Simpson%27s_paradox