In this study, we examined two research questions: (1) is high SES, as measured by high household income, high level of educational attainment, and being employed, associated with an increased risk of MDD; (2) is there support for the diminishing returns hypothesis, such that, an increased risk of MDD is observed among high SES compared to low SES individuals.
Regarding the first research question, we found no statistical evidence that high household income was associated with lower risk of MDD among any racial-ethnic group. The non-significant effect of household income on MDD suggests that income alone is not responsible for the increased risk of MDD (Williams et al., 2007b
; Blazer et al., 1994
; Weissman et al., 1991
). Epidemiologic data have demonstrated that although there are differences in the expression of depression symptoms across racial-ethnic groups, there are consistent similarities in the core features of MDD across racial-ethnic groups (Ballenger et al., 2001
; Simon et al., 1999
). Thus, a possible explanation for this finding may include the fact that the course and the consequential effects of MDD may be similar for those who suffer from MDD - irrespective of income level.
The non-significant effect of household income must be interpreted in light of a study design limitation. Our analysis reflects the cross-sectional association between household income and MDD. Longitudinal data analysis has shown that social causation, rather than social selection, may in part explain why low income individuals may be at increased risk for MDD (Ritsher et al., 2001
). However, studies have shown that causation and selection are not mutually exclusive processes and may both be influential over the life span (Nestadt et al., 1998
; Kessler et al., 2003a
). Unfortunately, the cross-sectional nature of our data precludes us from examining this causal pathway. This could, in part, explain our non-significant results.
For educational attainment and MDD, we found significant associations between a high level of education attainment and lower risk of MDD among White men. Among White women, there was a significantly reduced risk of MDD among those with less than 16 years of education. Despite these findings among Whites, similar patterns were not observed among the other racial-ethnic groups. A potential explanation for these findings may be that years of education, a traditional measure of social stratification, may effectively model the association between SES and MDD among Whites (Lynch & Kaplan, 2000
). Conversely, education may not translate to economic opportunity for racial-ethnic groups (Farmer & Ferraro, 2005
). This suggests that education as a measure of SES in this study, fails to capture the context in which SES may influence MDD. This finding further suggests the need to adopt modeling approaches that more accurately capture the context in which SES may influence MDD among different groups. One potential approach may be the inclusion of SES measures during both distal and proximal periods of the life-course, since early-life and contemporary SES have an influence on MDD (Mutaner et al., 2008
). Based on the cross-sectional nature of our data, it is not possible to determine whether assessment of SES at different time points during the life-course may be a modeling approach better suited to assess the association between SES and MDD among racial-ethnic groups. Future studies are needed to determine whether this modeling approach improves our understanding of the SES-MDD association among racial-ethnic groups.
Another potential modeling approach may be the inclusion of alternative measures of social stratification. Research suggests that the inclusion of “neomaterial” determinants (proximal physical or biological risk or protective factors) and “psychosocial” determinants (i.e. perceived social status) may be more instrumental in explaining the association between SES and MDD (de Castro et al., under review
). These determinants may be relevant in the association between SES and MDD because depression is clearly affected by sociopsychological risk factors that cluster among individuals of low SES (i.e. stressful life events) (Mutaner et al., 2004
). Additional studies are needed to determine whether these assessments of stratification are relevant to understanding the role of SES in MDD among racial-ethnic groups.
Our results also revealed an association between being out of the labor force and an increased risk of MDD among Whites and Latino men. In analyses by nativity, significant differences were present among both U.S.-born and foreign-born Latinos who reported being out of the labor force. These findings are consistent with earlier studies reporting that being out of the labor force was associated with 12-month MDD (Alegria et al. 2007b
; Kessler et al., 2003a
). Our findings suggest that being out of the labor force may adversely affect individual mental health due to the effects of economic hardship. In addition, environmental features of work postulated to promote psychological well-being (e.g., interpersonal contact, skill use, physical security, and valued social position) may also explain why being out of the labor force may increase the risk of MDD (Warr 1987
With regard to our second research question, we found no evidence to support the diminishing returns hypothesis
. Consistent with previous epidemiologic studies, we found a lower prevalence of 12-month MDD among Blacks, Latinos, and Asians compared to non-Hispanic Whites (Takeuchi et al. 2007
; Alegria et al. 2007a
; Williams et al. 2007a
; Breslau et al. 2006
; Breslau et al. 2005
; Kessler et al. 1994
). Our findings suggest that an increased risk of MDD was not observed among high compared to low SES individuals. Thus, despite the low prevalence of MDD among racial-ethnic groups, there is no empirical evidence to support that the association between racial-ethnic status and MDD varied by SES level. Previous research offers possible explanations for the protective factors (e.g., ethnic identification, social support) that likely result in the lower prevalence of MDD (Herd & Grube, 1996
; Mossakowski, 2003
) (Wallace & Forman, 1998
; Varon & Riley, 1999
; Ellison et al. 2001
; Lee & Newberg, 2005
; Williams & Neighbors, 2006
). Future studies should continue to explore the social context of racial-ethnic groups in order to understand why these groups experience a lower prevalence of MDD despite their economic disadvantage.
The findings from this study should be interpreted in light of several limitations. First, the survey was not translated into “other” Asian languages, which may have excluded from the study non-English speaking Asians who did not belong to target ancestry groups. Also, Caribbean immigrants included in the sample had to self-identify as Black as well as speak English. These restrictions may have excluded non-English speaking Caribbean Blacks. Consequently, findings are most generalizable to target Asian ancestry groups and English-speaking Black Caribbeans. Second, our analyses relied upon the WMH-CIDI instrument to document psychiatric disorders. Although this diagnostic instrument allowed us to compare MDD among racial-ethnic groups, the prevalence of the disorder among immigrant groups may have been underestimated, especially if immigrants expressed their problems in unique ways that were not identified by DSM-IV
. This may be a particular issue as culture can affect both the clinical presentation of specific psychiatric disorders and the ability to recall or report symptoms (Williams et al., 2007b
; Alegria et al., 2004
Despite these limitations, the findings suggest that the association between indicators of SES and 12-month MDD is complex as associations differed by racial-ethnic status, gender, and nativity. Future studies must continue to explore how socio-cultural statuses across the life-course influence how race-ethnic groups experience MDD, as well as other forms of psychiatric ill-health.