We tested 3 hypotheses-social causation, social drift, and common cause-regarding the origin of socioeconomic disparities in major depression and determined whether the relationship between socioeconomic status (SES) and major depression varied by genetic liability for major depression.Methods
Data were from a sample of female twins in the baseline Virginia Adult Twin Study of Psychiatric and Substance Use Disorders interviewed between 1987 and 1989 (n = 2153). We used logistic regression and structural equation twin models to evaluate these 3 hypotheses.Results
Consistent with the social causation hypothesis, education (odds ratio [OR] = 0.78; 95% confidence interval [CI] = 0.66, 0.93; P < .01) and income (OR = 0.93; 95% CI = 0.89, 0.98; P < .01) were significantly related to past-year major depression. Upward social mobility was associated with lower risk of depression. There was no evidence that childhood SES was related to development of major depression (OR = 0.98; 95% CI = 0.89, 1.09; P > .1). Consistent with a common genetic cause, there was a negative correlation between the genetic components of major depression and education (r2 = -0.22). Co-twin control analyses indicated a protective effect of education and income on major depression even after accounting for genetic liability.Conclusions
This study utilized a genetically informed design to address how social position relates to major depression. Results generally supported the social causation model.