(e.g., infant mortality, birth weight, asthma, and other respiratory conditions) are reviewed. Some of these population trends show health improvements across time; others point to increasing health problems. Behavioral and psychosocial factors are implicated in both. A major international data source on health trends is the set of Demographic and Health Surveys. 1 An overarching theme is that the maintenance and improvement of population health have been and continue to be due as much to changes in broader socioeconomic and environmental forces as to more microscopically based biobehavioral science. Understanding and facilitating improvements in socioeconomic conditions, general public health and sanitation, and private and public policies affecting lifestyle have accounted for the bulk of historical changes in population health and very likely recent advances as well (Rose, 1992).
Health varies substantially across and within countries. For example, in 1998 life expectancy in Sierra Leone was 37 years and in Japan it was 80 years. Ninety percent of this range, however, is covered by variation across counties within the United States. The range in life expectancy between females born in Stearns County, Minnesota, and males born in various counties in South Dakota is 22.5 years and extends to 41.3 years when race-specific life expectancy is calculated (WHO, 1999). Over time, life expectancy in the United States has risen from 47 years in 1900 to 78 years in 1995. Table 1 shows the changes in life expectancy at birth between approximately 1910 and 1998 in selected countries.
On average, people in richer countries live longer and have higher-quality lives than people in poorer countries. Within countries, at the city, county, and regional levels, people with higher socioeconomic status are on average in better health than those with lower socioeconomic status. As described in Chapter 7, there is also considerable variation across racial and ethnic categories that interacts with socioeconomic status.
Recent research shows clearly that chronic disease disability rates are falling in the United States. Figure 1 shows the proportion of the elderly who were disabled in 1982, 1984, 1989, and 1994. Disability is measured as impairments in activities of daily living (ADLs, such as bathing, toileting)
The data are available electronically: Demographic and Health Surveys: http://www.measuredhs.com.