Acute, episodic life events tell only part of the depression story. Another source of depression—although not as commonly studied—is exposure to enduring, long-term stressful circumstances. Many studies of stress-depression associations have not adequately distinguished between the effects of ongoing and acute stressors (e.g., Brown and Harris, 1978; Caspi et al., 2003), and failure to do so makes it difficult to fully explicate the mechanisms by which stressors have their effects on depression. An important feature of chronic stress, as with acute stress, is the bidirectional effect of stressful chronic conditions and depression on each other. The strains of poverty or unemployment or displacement in the case of immigrants and refugees, for example, may trigger depression, but depression erodes the individual’s ability to cope with or change his or her circumstances.
Another notable feature of chronic stress is that for many individuals there are multiple, related areas of chronic stress. Consider, for example, the association of several demographic predictors of major depression. Hasin et al. (2005) found that a major depressive episode was associated with being female, having low income, and being widowed, divorced, or separated. In addition, low educational attainment and being unemployed, disabled, or a homemaker are also associated with major depression (e.g., Kessler et al., 2003). Commonly, many of these conditions co-occur, with low educational attainment, low income, and disadvantaged work status related to each other, and being a widowed, divorced, or separated woman is likely to be associated with lower income.
A specific example of a chronically stressful condition amplified by co-occurring adverse conditions is single-mother status. Single mothers have been found to have higher rates of major depression than married mothers (e.g., Davies, Avison, and McApline, 1997; Wang, 2004), especially for separated or divorced compared with never-married mothers (Afifi, Cox, and Enns, 2006). Two large-scale studies have shown that the association between single-parent status and depression is entirely or largely mediated by higher chronic and acute stress and low social support (Cairney et al., 2003; Targosz et al., 2003). Yet the role of chronic stressors is neither simple nor straightforward. Lone mothers have higher risk of depression not only because of the presence of higher levels of chronic social stressors compared with two-parent families or even single parents residing with extended family but also because of their lower socioeconomic position. Furthermore, socioeconomic position might moderate the relationship between social stress and depression. For example, Barrett and Turner (2005) reported that among those with higher socioeconomic position, the adverse impact of racial discrimination and recent life events were more marked than that seen for those with lower socioeconomic position.