of differences in language, culture, and education among older people. Although differences in cognitive ability often mimic those in physical disability and disease, some differences do not fit this pattern. Hispanics perform worse on cognitive tests than might be expected given their life expectancy levels. In addition, previous results in this area have often been contradictory. This is partly due to reliance on nonrepresentative samples, but may also be due to tests for cognitive impairment that are not culturally sensitive. Traditional scales for indicating depression may also need to be modified for work focusing on older persons of different racial and ethnic groups (Turvey et al., 1999). Future developments in neuropsychiatric assessment and imaging techniques may help control for the effects of education and language in cognitive assessment.

Comparisons among groups, extending beyond the five major groups, might be useful in suggesting what aspects or consequences of racial and ethnic identity are really critical for health and disease and what additional dimensions should be measured. Some comparisons might involve multiracial or multiethnic groups. Study of black-white unions, for instance, suggests that the race of the mother is more important than the race of the father for infant health (Polednak and King, 1998). Other comparisons might involve racial and ethnic groups in other societies. For instance, immigrant groups in the United States lose their health advantage over time; this does not appear to be true in the United Kingdom (Nazroo, 2004), which raises important questions about mechanisms. To take another example, deaths from respiratory conditions in South Africa are considerably less common among blacks than whites (Bradshaw et al., 2004), suggesting a parallel with the U.S. situation and the possibility of investigating possible protective factors cross-nationally.

Why racial and ethnic differences in health exist is obviously a central issue for further research. The existence of some health differences may be clear, but their meaning is not. The relatively high mortality of blacks and the relatively low mortality of Asians and Hispanics give rise to several possible lines of investigation. Research on the selection of immigrants by health status may help clarify some differences involving these groups. Socioeconomic factors obviously differentiate groups and play a role in health differences, but how much of a role, and in what ways do such factors contribute? Differences at older ages require study of cohort selectivity and the effect of differential mortality on the characteristics of survivors. We consider these and other possible roots of differences in the following chapters.

Is there any basis, from looking at differences, for deciding which health differences especially need to be explained? Various plausible arguments might be made. For instance, it is important to understand the factors limiting the health of groups that are both relatively large and in the poorest

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