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Objectives
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| Introduction and Trends in 65+ Individuals in U.S | ||||||
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We have also seen the growth in the percentage of the population that is older than 65. This also has been growing for about a hundred years. In fact, we are at a point right now where it is not growing very quickly but by 2010, there will be a tremendous growth in this percentage in the U.S. (Figure 2). | ||||||
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Dependency Ratio: Definitions and Trends
Figure 3 indicates the trend in the dependency ratio in the United States from 1900 through 2050. In contrast to the other indicators of population aging, the trend in the total dependency rate is not consistently upward. In fact, total dependency declines over most of the 1960 to 2010 period and then increases sharply between 2010 and 2030. Note, however, that the total dependency level reached by the middle of the next century is roughly the same level we experienced at the middle of this century. This fact is one of the reasons why many demographers and economists are not overly concerned about the aging of the U.S. population because, in terms of dependency, we have already experienced levels similar to those in our future. Note, however, that the composition of the dependent population will be very different in the middle of the next century than it was at the middle of this century (Figure 4). In 1960 less than 20 percent of the dependent population was old; in 2050 the number of older and younger dependents will be roughly similar. As you can see this is because the number of dependents less than 18 has declined and will continue to decline. At the same time, the number of dependents over 64 has risen and will continue to rise until the year 2030. The reasons for this lead us to a general discussion of the factors affecting population aging. | ||||||
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| What Causes Population Age Structures to Change? Demographic Transition: Definitions  Population age structures change because mortality or fertility changes or because people move in or out of the population. Putting aside movement or migration for the moment, the changing age structure of the United States resulted from changes in mortality and fertility that have occurred over the past century. These changes in mortality and fertility are known as the Demographic Transition. The demographic transition is the change from high levels of both fertility and mortality to low levels of both fertility and mortality. In most countries the demographic transition began with a decline in mortality due to a reduction in deaths from infectious diseases. The beginning of the increase in life expectancy occurred before medical treatment could do much to save people from death. During the first half of the twentieth century, antibiotic and sulfa drugs were developed that provided a life saving treatment for those suffering from most infectious conditions. In the United States the demographic transition began in the nineteenth century with decreases in deaths from some once epidemic diseases like smallpox, cholera, and typhoid. It continued through the 20th century with the virtual elimination of deaths from other infectious diseases like measles, scarlet fever, diphtheria, and polio. Tuberculosis, once a major cause of death in this country, had been largely eliminated until a recent regrowth. Until the development of AIDS as a major cause of death for young people in the late 1980s, there was hope that deaths from all infectious diseases would be minimal in our society. This remarkable conquest of infectious disease was accomplished largely through public health measures.
Edward Jenner began the public health revolution by administering the first vaccine against smallpox to prevent the disease. The use of this vaccine spread throughout the world during the nineteenth and twentieth centuries so that this is the one disease that is now regarded as eliminated. In the second half of the nineteenth century, Louis Pasteur developed the germ theory of disease and Joseph Lister demonstrated how the use of antiseptics could prevent the transmission of some diseases. These basic biological discoveries were the root of the public health movement which was begun in cities in the U.S. (and other countries like the U.S.) near the turn of the twentieth century to combat the very high mortality rates experienced under increasingly crowded living conditions. The public health movement concentrated on preventing the spread of infectious diseases through street cleaning, water purification and chlorination, personal hygiene and the isolation of persons infected with contagious diseases. The movement also encouraged the use of vaccinations and immunization as they became possible. The reduction in infection may have been aided by the development of refrigeration, pasteurization of milk, and the more rapid shipping of perishable foods due to the development of railroads.
All of this contributed to a decline in mortality from infectious diseases which were the leading causes of death in preceding centuries. The conquest of infectious diseases had its greatest impact on the youngest segment of our society. It was these weaker members of a population who were most susceptible to infectious disease. During this period the expectation of life at birth - or the average age at which someone died - increased from about 40 years to about 50 years. Most of the increase came from the fact that people survived childhood rather than that they lived after 40. | ||||||
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| Mortality: Death Rates and Trends The reason to provide this detailed history of mortality decline is two-fold: it is the foundation for the demographic change that causes the aging of our society and it indicates how much of the change in life expectancy and the reduction of mortality occurs because of an increase in basic scientific knowledge with public health applications rather than medical treatment as we know it today. By the second part of this century - after 1950 - we had dramatically reduced death from infectious disease. As a consequence, deaths after that point were largely concentrated in the diseases that kill people after many years - chronic conditions - and at older ages. The most important of these are heart disease and cancer. It was during the second part of the twentieth century that science set out to understand and "cure" these diseases. This lowering of mortality, especially among the young, resulted in more children surviving and people having larger surviving families. Infant mortality was very high before this century with as many as a third of children dying before reaching adulthood. People eventually reacted to this increased survival of children by reducing their fertility, or having fewer children per family. The early reduction in mortality also coincided with the industrial revolution when countries changed their means of production from agricultural to industrial or from farms to factories. This also meant that people moved from farms to towns and cities and that people began to work for large companies rather than be self-employed. All of these changes also contributed to the reduction in the number of children. Lots of children were less compatible with urban industrial life than with rural agricultural life. | ||||||
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Fertility: Birth Rates and Trends Fertility was reduced so that the average family had 2 children during the 1930s (Figure 6). Again, this is important because it shows that people could have small families even before the age of modern contraception. It also sets the stage for a period when fertility was very responsive to economic conditions which is one of the reasons the United States is experiencing special circumstances in its aging in the next century. We will return to this topic at the end of this section. This reduction in fertility is the basic cause of the aging of our society. Fewer babies have been born resulting in fewer young people. When we look at population aging, we are really looking primarily at the effect of decreases in fertility. Decreases in fertility reduce the number of young people and if the fertility rates stay constant for some period of time, the population will acquire a fixed age structure that is older. The future age structure of the United States, and other countries depends primarily on what happens to fertility rates in the future. | ||||||
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How Mortality and Fertility Combine in Population Aging
We should note here that over the last thirty years of the twentieth century, major decreases in death rates from heart disease have fueled a remarkable decline in mortality at the oldest ages. These decreases in deaths from heart disease have been caused by a variety of factors including better diagnosis, better surgical and drug treatment, better emergency treatment, specialized hospital treatment, and better lifestyles. While deaths from cardiovascular conditions have been reduced tremendously, cardiovascular disease and cancer remain the major causes of death in our society. We have not seen the same improvement in cancer death rates over the past thirty years as we have experienced for heart disease and stroke. Some cancer death rates have been reduced and some have risen. These causes of death will remain our challenge in the next century. We noted above that the United States had special fertility circumstances that will affect its population aging in the next century. We had a reduction in our fertility rates from high to low in the 1930s (see figure above). The low level of the 1930s was in reaction to a severe world-wide economic depression. People felt that they could not adequately provide for children so they had fewer. Fertility was also relatively low during the 1940s due to the involvement of the United States in World War II. After the war, however, fertility rates went up dramatically, both to make up for lost time, and in response to the period of rapid economic expansion after World War II. From 1946 through 1964, the United States experienced a baby boom. Large numbers of babies were born. These babies eventually became children and adults. Bill Clinton is known as the first "baby boomer" president. He was born in the vanguard of the baby boom. The special aging issue for the United States is that the baby boom will age into the ranks of the older population after 2010.
Recall the aging of the U.S. population described in the beginning of this lesson: the increase in the numbers and the proportion of older people. The sharp increase in the numbers and proportion of older people after 2010 results from the aging of the baby boomers. Recall the dependency ratio trends (Figure 3 and Figure 4). Youth and total dependency ratios were very high during the 1960s. When families became smaller and some of the baby boomers aged past 18, total and youth dependency ratios decreased during the 1970s and 1980s. When the baby boomers become older after 2010, they are going to increase the percentage of old-age dependents and reduce the percentage of the working age population. The same people who contributed to our high dependency ratio as youth in the 1960s will contribute to the increasing dependency ratio as seniors after 2010. Because the baby boom the American aging experience has been somewhat different from other countries. We experienced the largest baby boom after World War II; this first delayed our aging more than that of other countries and will eventually cause it to occur more rapidly than in some other countries. | ||||||
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| Where Has Population Aging Occurred? Population aging is a world-wide phenomena now. This is because fertility has begun to decline around the world. The countries that have aged in a fashion roughly similar to that of the U.S. include all of Europe, Australia, Japan and Canada. These countries are known as the "developed" countries because they have experienced economic development in a fashion similar to that of the United States. Countries that are just beginning to age include Taiwan, China, Thailand, Malaysia, and India. These countries are known as the "developing" countries as they are currently still undergoing the process of changing from an agricultural to and industrial economic base. Countries like the U.S. have experienced aging over the last 100 years during which we all went through the process of industrialization and the demographic transition. Countries in Asia, South and Latin America, and more recently Africa have begun their demographic transitions later. The aging transition in these countries, like the demographic transition, is going to occur much more rapidly. Countries like the U.S. took generations to go from high to low fertility. China, the most rapidly aging of countries, went from high to low fertility in the time of less than one generation. Rapid fertility decline in a population contributes to rapid aging some years later. Because fertility is now declining most rapidly in Asia, Asia is the fastest aging continent. Africa will probably be the most rapidly aging continent in the future. | ||||||
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Key Points
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Monday, June 13, 2011
Demographics of An Aging Population
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