The obvious problem you run into with twins raised apart is that there in fact aren't many twins who are raised apart.

From tfa

> We estimated uncorrected heritability (uncorrected for extrinsic mortality) (materials and methods) in three independent ways: (i) MZ twins reared apart (n = 150), (ii) DZ twins reared apart (n = 371), and (iii) MZ versus DZ twins reared together (196 MZ, 325 DZ)

This is from _one_ of the datasets they examined, but there were also two others. n=150 twins reared apart in their small category, or n=520 twins reared apart total is the lower bound of data they had, and even that is not too shabby imo

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tptacek 6 hours ago | parent [-]

I don't have an opinion to offer here other than the intrinsic limitations of studies that depend on twins raised apart (that there aren't many of them). It's an unusual instance of a stat where the obvious concern with the premise is underappreciated rather than overappreciated. I've got nothing on MZ/DZ controls.

	▲	pinkmuffinere 6 hours ago \| parent [-]
		ah I see, you're commenting on the general difficulty, not necessarily saying this study's results are bad due to the limitation. My apologies, I don't think we disagree.