Adoption studies help to investigate the nature /nurture debate in psychology, that is they help to explore the extent to which a certain behaviour may be caused by genetic factors as opposed to environmental factors.
Let’s take schizophrenia as an example. If we want to explore whether schizophrenia has a genetic component we can look at the concordance rate for biological parents with schizophrenia and their adopted-away offspring (e.g. what is the frequency of the adopted child having schizophrenia when they have a biological parent with schizophrenia?) and compare this with the concordance rate for biological parents without schizophrenia and their adopted-away offspring (what is the frequency of the adopted child having schizophrenia when they do not have a biological parent with schizophrenia).
Another possibility would be to compare the biological and adoptive parents of offspring who have been adopted and have schizophrenia; if schizophrenia was genetic we would expect a higher concordance rate between offspring with schizophrenia and their biological parents than their adoptive parents.
The naturally occurring IV, if you like, is whether the person they are being compared with shares DNA with them or not. This is a naturally occurring variation divided into two levels/condition, ‘Yes’ they do share DNA (bio parents), ‘No, they don’t share DNA (adoptive parents). For example, researchers might look for the percentage of biological parents who also have schizophrenia and the percentage of adoptive parents who also have schizophrenia. If schizophrenia has a genetic component we would expect children to be more like their biological parents than their adoptive parents, e.g, a higher concordance rate.
Adoption studies are more like a correlational study than an experiment as we are not controlling anything at all, we are simply looking to see whether there is a relationship between having schizophrenia or not and being the biological parent or not. This 2 x 2 frequency table should hep you to get your head around this (I just made the figures up so you cold see how the results table might look).
| Biological parents | Adoptive parents | |
| Does have schizophrenia | 16 | 2 |
| Does not have schizophrenia | 5 | 14 |
Some adoption studies have also looked at the quality of the adoptive family that the children are being adopted into and rated this. Studies have found that children are only more likely to become schizophrenic when they are adopted into a more dysfunctional home, if they also have a genetic predisposition towards schizophrenia, as indicated by having a biological relative with the condition. Tienari (2004) is an excellent example of an ongoing adoption study in Finland which look at just this: http://bjp.rcpsych.org/content/184/3/216.full the study is excellent for illustrating the diathesis-stress model of schizophrenia.
Practice Questions:
| Fill in the gaps:
Adoption studies are used to assess if a characteristic is the result of ………………………………………………. or of …………………………………………………… This is done by comparing the children to their ……………………………….. parent |
- Explain one reason that a psychologist might choose to conduct an adoption study (2)
- Explain how a psychologist could use an adoption study to research whether schizophrenia has a genetic component (4)
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