ethnic group share a unique history different from that of other ethnic groups (American Anthropological Association, 1997; Zenner, 1996). Usually, a combination of these features identifies as ethnic group. For example, physical appearance alone does not consistently identify one as belonging to a particular ethnic group; individuals belonging to certain ethnic groups may vary widely in physical appearance (e.g., skin color and hair texture), but they share a common ethnic identity. In the U.S., there are "macro" ethnic groups, such as Latinos or Hispanics, which have many sub-groups, such as Mexicans, Mexican Americans, Cubans, Puerto Ricans, and so on. "Race," in contrast, represents a social or cultural construct of human variability based on perceived differences in biology, physical appearance, and behavior (American Anthropological Association, 1997; Smedley, 1999). The problems with the concept of race for purposes of health research will be discussed later in this chapter.

It is useful in medical and epidemiologic research to distinguish ethnic groups from one another, provided that researchers are clear on the nature and source of human variation (e.g., cultural and behavioral patterns, environmental influences) and their relationship to health outcomes. Membership in an ethnic group may be associated with behavioral and environmental factors which may increase or decrease the likelihood of illness. Thus, the availability of pertinent information for a diversity of ethnic groups would assist both those involved in health research and the population as a whole by indicating if any ethnic differences need to be further explored. Such research, however, can be accomplished only by clearly identifying population groups and understanding that human identity is not static or mutually exclusive. Ethnicity can be a product of interaction between people of different origins and identities. The "boundaries" of ethnic identity, however, are still unclear. Some may identify themselves as belonging to a particular group in one context, and to another group in a different context. "Identities thus become circumstantial" (Zenner, 1996, p. 394). Ethnicity is more flexible, fluid, or perceived, than rigid or fixed. This has been compounded by the increased number of mixed ethnicity families in this country, where individuals may claim two or more ethnicities, or give different ethnic identifications at different times or for different purposes. This makes the proposed revisions for the year 2000 census all the more important, as federally sponsored health research will need to account for individuals who identify themselves as from diverse backgrounds.

In the study of cancer, considerable attention has been given to "minorities" as a group, but medically underserved individuals make up a