There are numerous possible problems that can be brought about in relation to the clarification and understanding of these studies. The crucial identical setting assumption theorizes that monozygotic and dizygotic twins are similarly connected in their contact to ecological actions of etiologic significance to major depression. The larger resemblance between monozygotic as opposed to dizygotic twins for major depression might result from ecological influences and not genetic features if this were not the case. Equal environment issues and limitations have been studied on several occurrences and there are indications that support the legitimacy. Assumptions about major depression from twins may not simplify to singletons if there are detailed
