It is my understanding that due to ethical concerns, the scientific field of psychology does not have a data collection methodology capable of distinguishing between effects caused by the parents' genes and effects caused by the parents' actions, and as such, no possible statistical approach will give a correct answer on the heritability of traits caused by the latter, like schizophrenia a.k.a. religion or intelligence. In order to clear up my "misunderstandings and ignorance", you will need to demonstrate an approach that can, at the very least, successfully disprove genetic contribution in circumcision.
I think you need to read up a little more on behavioral genetics. To point out the obvious, besides adoption studies (you might benefit from learning to use Google Scholar) and and more recent variants like using sperm donors (a design I just learned about yesterday), your classic twin study design and most any 'within-family' design does control for parental actions, because they have the same parents. eg if a trait is solely due to parental actions, then monozygotic twins should have exactly the same concordance as dizygotic twins despite their very diff... (read more)
Your understanding looks silly. It is rather obvious that not all children are brought up by their parents and that has been used in a number of studies. In fact, many classic identical-twins studies rely on being able to find genetically identical people who were brought up in different circumstances (including different parents).
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
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