Research in many societies has revealed higher rates of psychopathology among people of lower SES than people of higher SES. For adults, SES is typically measured in terms of the adults’ educational and/or occupational attainments.

The importance of SES is not merely as an index of income, as higher rates of psychopathology are associated with low educational and occupational attainment even in societies where incomes are fairly uniform. The following hypotheses have been proposed to explain elevated rates of major psychopathology, such as schizophrenia, among lower SES adults: (a) The downward-drift (or social-selection) hypothesis, which posits that disturbed adults drift down the SES ladder because their psychopathology prevents them from attaining and maintaining SES levels that would be expected from their parents’ SES levels; and (b) the social-causation hypothesis, which posits that low SES environments increase risks for psychopathology.

The downward-drift hypothesis and social-causation hypothesis are not mutually exclusive: Each hypothesis could help to explain elevated rates of different kinds of psychopathology among lower SES adults. However, downward drift cannot explain elevated rates of psychopathology among lower SES children, because their SES levels are not dependent on their own educational or occupational attainments. Consequently, social causation factors can be tested more directly by tracking psychopathology from childhood to young adulthood than in adulthood.

Wadsworth and Achenbach (2005) did this in a U.S. national sample of children and adolescents who were initially assessed at ages 8 to 17 years and were then reassessed at 3-year-intervals for 9 years. Parents initially rated the subjects on the ACQ Behavior Checklist, which included 115 problem items from the CBCL. At subsequent reassessments, parents rated the subjects on the CBCL until age 18 and then on the Young Adult Behavior Checklist (YABCL). For low SES subjects, standardized problem scores rose significantly across the subsequent assessments for all syndromes except Withdrawn. By contrast, the problem scores of higher SES subjects did not change significantly. Equally important, all significant increases in the proportions of subjects with clinically elevated scores (>1 standard deviation above the mean) were in the low-SES group. This means that the new incidence of clinically elevated scores on all syndromes was significantly greater for low SES than higher SES subjects.

Over the 9 years of the study, the cumulative prevalence of clinically elevated scores was significantly higher for low SES subjects than for higher SES subjects on the Withdrawn, Thought Problems, Attention Problems, Delinquent (now called Rule-Breaking) Behavior, and Aggressive Behavior syndromes. In addition, significantly lower remission rates were found for low SES subjects on the Withdrawn and Somatic Complaints syndromes.

Although genetic liabilities and other factors are apt to contribute to psychopathology, the findings indicate that low SES was associated with progressive increases and lower remission rates for several forms of psychopathology from childhood to adulthood. The lower remission rates might be explained by the finding that the elevated incidence of psychopathology among lower SES subjects was not accompanied by higher rates of mental health service usage.

Reference: Wadsworth, M.E., & Achenbach, T.M. (2005). Explaining the link between low socioeconomic status and psychopathology: Testing two mechanisms of the social causation hypothesis. Journal of Consulting and Clinical Psychology, 73, 1146-1153.