Comment by tripletao

> Unless your classifier is not independent from the base rate - that is, a classifier that gets more lenient if there's more fraud in the group.

If I understand correctly, that was the purpose of their "reweighting". To remove "bias" from their new model, they looked at the aggregate false positive rates by nationality, then applied explicit penalty to people with Western nationality to bring that FPR equal to non-Western.

I'd certainly agree that's undesirable, and my point was also to highlight that (since the article was reasonably clear on the type of fairness they achieved, but much less clear on the fairness they sacrificed).