Part 2: World and U.S. Populations

   
   
   

Population Pyramids

Before turning to the implications of population aging, we have one more graphical approach to examining the age structure of a population - the Population Pyramid. In this section we will also introduce the effect of migration on the age structure of a population, a process that we have ignored to date. 

A population pyramid represents the age and sex structure of a population using bar graphs to represent the percentage or number of people in each age-sex group. In contrast to a typical bar graph, the graphs are on their sides with the axis in the middle. This means that they often take the shape of "pyramids" as the size of the population in the upper ages is smaller than that in the lower ages. This graph allows one to compare the relative size of age and sex groups at a glance.

World Population Expansion

   
 

 
   

Developing and Developed Countries

To begin with, let us examine population pyramids for typical "developed" and "developing" countries of the world in 1990. These figures very graphically indicate the different age structures for the two sets of countries. The developing countries have a population structure that resembles a pyramid with a broad base of young and a small apex of old. Mexico in 1995 is an example of a pyramid for a developing country.

 


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The developed countries are beginning to lose their "pyramidal" shape as they become more straight up and down with almost equal numbers of people in adjacent age groups until the ages of high death rates begin after age 65. Finland in 1996 is an example of a pyramid for a developed country. 


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Japan in 1996 provides another example of a population pyramid for an even older and less pyramidal developed country. 


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United States

Now to turn to the United States. View the United States population pyramids for 1900, 1960, 1980, 2000, 2010, and 2030. Over time, the pyramid changes from a "pyramid" to a  sky scraper or an  "empire state building" shape. This is the kind of change that all societies like the U.S. have experienced. Notice how the bulge of the baby boomers impacts successive U.S. pyramids. Imagine the problems connected with providing schools for this group of people in 1960, jobs in 1980, and houses in 1990. These are the people who will be eligible for Social Security between 2010 and 2030. By 2030, many of them will have died out as the earlier baby boomers will be over 85 than, and the population - barring any unexpected changes - will have age groups of roughly similar size up to older ages. At the older ages, the pyramids indicate not only the decreasing numbers of people but also the preponderance of females that occurs at the oldest ages. This "feminizing" of the population as it gets older is due to sex differences in mortality. This will be described in more depth in later sections of the course.

   
   
   

Population Pyramids of the U.S



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Exercise: The "Baby-Boom" Generation
   
   
   

Special Population Pyramids

1946 Germany, population pyramids are a good way of spotting unusual circumstances in the composition of a population. Examine the population pyramid for Germany in 1946. The pyramid indicates that there were fewer young men then young women. This was of course the result of the loss of life incurring during World War II. There were also fewer births after the war due to the shortage of men.


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    United States

Unusual sex and age distributions can also be shown for smaller geographic areas. View the population pyramids for Florida, Arizona, and Alaska in 1990. These three states are quite different in composition by sex and age. Their differences are not due to differences in fertility and mortality, which we have discussed as the source of population age structure differences to this point, but to differences caused by migration.

States like Alaska become young because working age people move to them for jobs. This is true for other states in the Northwest like Washington and Oregon; parts of the West; and even parts of the East like Washington and Boston.


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Before leaving the topic of the age structure of various areas, let us think a bit about what causes states in the United States to have such different percentages of older people like Alaska and Florida. As you have guessed above, these states have acquired different age structures from the age differences in their migration streams. The old have moved in large numbers to areas of moderate climate like the South and the Southwest. This migration depends not just on climate but also on the relative price of houses and the availability of services, friends, family, and recreation. This means that states like Florida and California were once the primary destination of older migrants. Now Arizona, Nevada, Arkansas, North Carolina and other states are receiving migrants from the Northern and Mid-Western states. These states tend to become somewhat older as these people move in and the states older population may age as the migrants age. This has happened in Florida and is happening in Arizona.


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Exercise: Investigate Population Information about Your State and County

   
   
   

Special Population Pyramids: Retirement Communities

There is a whole set of states and areas that age not because old people move into them but because young people leave them. This has been true of the Midwest for decades as young people were less and less likely to go into farming. Many rural areas of this country have older populations because young people have left these areas in search of economic opportunities and the rest of the population has "aged in place".

Migration can make populations of areas smaller than states have very different age structures. Examine the age structure of Sun City, Arizona, in 1990. This was one of the early retirement communities that sprang up in a desert areas of the Southwest over the past two decades.


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Special Population Pyramids: Los Angeles

Towns and areas that are not experiencing any circumstances as obviously dramatic as those of Sun City can have very different population age structures and this is demonstrated by differences in their population pyramids. Look at four parts of the Los Angeles Metropolitan Area in 1990.


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East Los Angeles is an area with a relatively low level of education and income and a large number of immigrants from Central and South America. Immigrants tend to be in their 20s. People who are in their 20s are most likely to have children and immigrants tend to have a slightly larger number of children than those who are native born. East Los Angeles has a very young population. This neighborhood would have a high need for child daycare services.


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Everyone knows that 90210 - Beverly Hills - is an area where wealthy people live. Beverly Hills is an established suburb of Los Angeles, which developed many decades ago. This population may have relatively fewer children, smaller families, and they are much older than people in East Los Angeles. This area requires many senior services.


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The 20 somethings live in Marina Del Rey or "The Marina" as it is called in L.A. This is an area of apartments and condos, bars and restaurants, and a single life-style. There are very few people who are either very young or very old in the Marina. This is more likely to be a place where the television version of the "90210" group lives. If you wanted to start a dating service, Marina Del Rey would provide a population likely to use this service.



La Canada is a growing suburb on the fringe of Los Angeles. It has expensive homes and good public schools. It attracts families who can afford such homes; thus, its population is concentrated in the older middle ages. These families have children who are high-school age or younger. La Canada might be a good place to locate if you were an orthodontist.

Population pyramids can be constructed for any area for which population data can be gathered. They are useful indicators of the current state of the population structure. As you can see, you need some knowledge of historical events to see how a population attains structure. This is a useful tool for people involved in planning, developing, or delivery of goods and services.

   
   
   

Infant Mortality Rates

Despite the revolution in public health, the U.S. continues to have one of the highest infant mortality rates among industrialized nations. Click above for some more information on infant mortality rates for different countries.

   
   
   

Why Does the Age Structure of a Population Matter?

If people did exactly the same thing at all ages or had exactly the same needs and abilities at all ages, the age structure of the population would not make much difference. The relevance of the age structure is based on the fact that people of different ages have different needs, abilities, responsibilities, and entitlements. Some of this is related to biological changes that are related to chronological age itself. For instance, it would not be possible for very young children to survive without the help of some older members of society. Children need to be taught to become self-sufficient. It is also possible that a small number of very elderly and infirm people could not survive without the help of younger members of society. On the whole, however, the importance, of age differences arise because of the societal expectations and societal circumstances that determine what one does at a given age and what one is entitled to at a given age. Very few people younger 20 support themselves because many remain in school after that age. This is not because of a physical need to be dependent but because in an advanced technological society there is a need to have extensive training before undertaking many positions. At the other end of the age range, most people over the age of 64 receive some government support in the form of Social Security income and also most receive medical care under the government sponsored program of Medicare. This is not because of some physical necessity linked to age but because of societal arrangements whereby entitlement to certain programs is linked to age. The meaning of the age composition of a country is thus determined in good part by the social and political arrangements in that country.

These are also the circumstances that determine the meaning of changes in the dependency ratio and the importance of having young and old dependents. Let's examine what can happen to the dependency ratio under a variety of hypothetical circumstances.

Earlier we looked at the young dependency ratio assuming that everyone under 18 was dependent. This isn't very realistic for our society where higher education even beyond college is becoming the norm. Let's assume that people are dependent at least up until 22 and see what that does to the number of projected dependents.

At the other end of the age range, age 65 is no longer even a reasonable age to assume that dependency starts. The modal age of retirement is now about 62. If we assume that dependency starts at age 62 versus 65 what does this do to the number of dependents. What if the age at retirement goes up to 67 as will be encouraged by changes in social security rules coming into effect after 2000? What if people become dependent at age 72?

The exercise below shows that it is the age at which dependency first ends and then starts again that determines in large part the challenge of dealing with a changing age structure. The population age structure is not deterministic it just provides a setting within which people can determine a set of social policies and expected behaviors.

Critical Thinking E-mail Exercise