separate group that cuts across all ethnic groups. The term "medically underserved" is sometimes used to include underinsured or uninsured people; those with low levels of education; rural and inner-city populations; unemployed people; or those with low socioeconomic status (SES). As noted below, no consistent definition of "medically underserved" populations appears in the NIH descriptions of this construct.

Social class is traditionally measured through socioeconomic indicators such as education, income, and occupation (Adler et al., 1994). Many problems have been linked to low SES such as crime (Reiman, 1997), ill health (Pincus and Callahan, 1995), poor education (Levine and Nidiffer, 1996) and inadequate access to health care. Criticism and controversy have existed over which indexes have appropriately or inappropriately assessed SES to characterize social determinants of health. Schneider (1986) criticizes the use of common measures of SES such as Hollingshead's Four Factor Index of Social Status and Duncan's Socioeconomic Index for all occupations, noting the paucity of information on household patterns, social relationships, and the historical context of people's lives, all of which are factors that may mediate social status. Schneider advocates the use of an index that includes race or ethnicity, a detailed work history, autonomy, and decision-making authority. Lillie-Blanton and LaVeist (1996) agree that these factors in one's social environment (including power arrangements such as political empowerment and individual and community control and influence) are related to one's physical and mental health. A person may be working or living in an environment that exposes him or her to toxins that directly affect health, yet social relations and the conditions of one's neighborhood and work environment can also affect health. The latter experiences may shape the sense of "self worth, influence linkages to social structure and develop adaptive skills" (Lillie-Blanton and La Viest, 1996, p. 85).

Many researchers have made the mistake of attributing the health disparities between groups to race or ethnicity without paying close attention to socioeconomic variability. Lillie-Blanton and LaVeist (1996) explain the social context of health by describing an individual's SES as an "expression of the educational and economic opportunities available in one's social environment" (p. 84). They suggest that SES may be more relevant than race or ethnicity in assessing one's socioeconomic context or social environment. This approach not only incorporates the individual, but also incorporates the social forces that also affect individuals and their health.