I am not aware of non-anecdotal results here and I would be interested in seeing them - of course many CoC proponents will say that it's the right thing to do whether or not it produces a more technically meritorious project and this is legitimizing the view of a meritocracy, but I am personally expecting the answer to be that the project will in fact be more meritorious, and I think data would go a long way to arguing against (what I perceive as) biases and gut feelings against Contributor Covenant-like CoCs masquerading as data-driven concerns.