So... does it mean that it's completely irrelevant who adopted Harry Potter, because the results would be the same anyway?
In the context of IQ I've seen it claimed that normal variation in parenting doesn't do much, but extreme abuse can still have a substantial effect. So parenting quality would only make a difference at the tails of the parenting quality distribution, but there it would make quite a difference.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
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