A new study from the American Journal of Public Health used a large population-based sample of twins to examine why incidents of major depression are more common among those with lower socio-economic status.
The study tested three potential hypotheses to explain the relationship:
- social causation which predicts that lower socio-economic level leads to stress and adversity, which in turn increases risk of major depression
- social drift which predicts that those with major depression are less likely to transition out of, or more likely to transition into, lower socio-economic status
- common cause which predicts that some shared risk factor, either genetic or environmental, could increase risk for both major depression and lower socio-economic status.
Findings aligned with the social causation hypothesis, even after accounting for genetic influence. There was also modest support for an interaction between genetic propensity for depression and the social environment, such that the relationship between low socioeconomic status and development of depression was stronger for those with higher genetic risk.
“As we illustrated, twin samples offered a means to examine the joint action and interaction between genetic liability and the social position,” the study’s authors concluded.
Integrating Social Science and Behavioral Genetics: Testing the Origin of Socioeconomic Disparities in Depression Using a Genetically Informed Design.