In your studies of biological psychology, you will have learned about one adoption study - AQA - A-Level Psychology - Question 8 - 2021 - Paper 1

One strength of Heston's study is that it involved careful matching of the 47 participants born to schizophrenic mothers with a control group. The matching was done based on sex, type of eventual placement, and length of time in child care. This allowed Heston (1966) to be more confident that the presence of schizophrenia was the only variable affecting the participants and the controls.

A significant weakness of Heston's study is that it found a relatively low 10.6% concordance rate which does not provide ample evidence or conclusive results regarding genetic predisposition and schizophrenia rates for adopted children. Moreover, there are other variables, such as drug use, that could have influenced the mental health of the children who were adopted away from their birth family.