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In a adoption study by ( Heston, Gottesman and Shields ), ( 16, 50, 15 )% of the children ,from 47 schizophrenic mothers, who had been adopted at birth had schizophrenia. This is much higher than the ( 1, 10, 50 )% population level. Therefore it seems that schizophrenia is ( hereditary, the result of environemental factors ). This is more conclusive than the twin study by ( Gottesman and Shields, Heston ) because the children ( didn't share, shared ) the same environment with the mother. However this study suffers from a ( small sample size, low ecological validity ).