Unlike twin studies, in adoption studies individuals are exposed to a different environment to their biological or genetic relatives. This makes it easier to separate genetic and environmental factors.
These studies are not easy to undertake as information on an adoptee and their biological families may not be available.
There are ethical issues to be considered when approaching members of the biological family, about a child who was adopted many years ago.
Adoption is not a random process, meaning that children are often placed in families resembling their biological family or in families that have been specially selected for other reasons.
Adoption is also an unusual event in itself, leading to a small sample size.
Interactive tutorial
To view this interactive tutorial, you need the latest Flash player.