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Gottesman and ( Shields, Shield, Shhhh, Samantha ) (1996) studied ( 61, 60, 90, 65 ) MZ or DZ twins. Concordance rates for MZ twins was ( 42%, 45% ) (but in severe cases of SZ concordance rate was ( higher, lower )). Concordance rates for DZ twins was ( 17%, 20%, 3% ).