Specifying race-ethnic differences in risk for psychiatric disorder in a USA national sample.

Social adversity is commonly associated with increased risk for psychiatric disorders (Dohrenwend, 2000). However, community studies in the United States have not found elevated point prevalence of psychiatric disorders among disadvantaged racial and ethnic minority groups (Kessler et al., 1994; Somervell et al., 1989), despite higher levels of social adversity experienced by these groups (Clark et al., 1999; Turner & Lloyd, 2004; Williams, 1999). In the National Comorbidity Survey (NCS), the first nationally representative survey of psychiatric disorders conducted in the US, we showed that the lower than expected point prevalence of DSM-III mental disorders among racial-ethnic minorities was attributable exclusively to differences in lifetime risk of these disorders as opposed to course of illness. Indeed, the course of illness tended to be more persistent among minorities than Non-Hispanic Whites in that study (Breslau et al., 2005). Thus, understanding reasons for the lower risk of ever developing a mental disorder appears to be the key to understanding the lower than expected prevalence of mental disorders among disadvantaged racial and ethnic minority groups in the US. In this report we take the next step towards identifying causes of race-ethnic differences in lifetime risk of psychiatric disorders by specifying these differences in greater detail with respect to clinical and sociodemographic characteristics. Using data from a recent national survey, the National Comorbidity Survey Replication, we investigate variation in race-ethnic differences across 1) individual DSM-IV disorders, 2) age of onset of disorder, 3) birth cohorts, and 4) educational attainment. Results of these comparisons will help guide the investigation of potential protective factors that result in lower lifetime risk among race-ethnic minorities. Our previous report considered race/ethnic differences in 3 broad classes of disorder: mood, anxiety and substance use disorders. However, it is important to know whether the differences we observed are consistent across disorders within these classes, implicating protective factors with generalized effects, or whether they are attributable to differences in a small number of disorders, implicating factors with disorder specific effects (Aneshensel et al., 1991). In this analysis we test for variation in race/ethnic differences across individual disorders within each class of disorders. In addition, we examine an additional class of disorders, impulse control disorders, that was not included in the earlier survey. Specifying race-ethnic differences in early vs. late age of onset of disorder can help identify the developmental periods during which protective factors exert their influence. If, for instance, reduced risk of psychiatric disorder begins with early onset disorders, we should consider protective factors present in childhood environments rather than adult social experiences. It has been suggested that stressors associated with minority race-ethnicity vary across the lifespan; minority children may be sheltered from the negative impact that discrimination in labor markets and other areas of adult life has on mental health in adults (Gore & Aseltine, 2003). This hypothesis predicts that the lower risk among minorities will be stronger for early than for late onset disorders. Specification of race/ethnic differences with respect to birth cohorts can help identify causal factors by locating the differences historically. This is of interest because the social conditions affecting minorities in the US have changed in recent decades in ways that influence the experience of social adversity, such as income (Levy, 1998) and educational attainment (Kao & Thompson, 2003). However, studies using distress scales have found that race/ethnic differences have not varied from the 1950s through the 1990s despite these changes (Thomas & Hughes, 1986). We do not know the extent to which the same is true for lifetime risk of psychiatric disorders. Continuity in race/ethnic differences across birth cohorts would point to factors that are transmitted across generations despite historical changes in social conditions. The association of disadvantaged minority status with lower lifetime risk of disorders suggests that the relationship between socioeconomic status and risk of onset may vary across race/ethnic groups (Williams, 1997; Williams et al., 1992). Two theories of such variation have been suggested. First, the ‘double jeopardy’ theory suggests that morbidity will be particularly elevated among low SES members of disadvantaged minority groups. This theory was supported by studies using distress scales that found higher levels of distress among Non-Hispanic Blacks relative to Non-Hispanic Whites only among those with low SES (Kessler & Neighbors, 1986; McLeod & Owens, 2004). Second, the ‘declining returns’ theory predicts the opposite pattern, with higher morbidity among minority groups at higher levels of SES. This theory, suggested by studies which found that minorities have lower economic returns to investment in educational credentials (Chiswick, 1988), has been supported in research on indicators of general physical health (Farmer & Ferraro, 2005). With respect to mental health the ‘declining returns’ pattern is also consistent with the suggestion that social stressors are most severe for middle class minorities who have the highest expectations but also face the most severe competition in labor markets (Cole & Omari, 2003; Jackson & Stewart, 2003; Neckerman et al., 1999; Parker & Kleiner, 1966).