SSRIC Teaching Resources Depository
Exploring the US Census
Eugene Turner, California State University, Northridge

Exercise 3 -- Describing the Age of Populations

© The Author, 1998; Last Modified 17 August 1998

Databases:  USCOsp.por; bgatsp.por

In this exercise you will use a few of the measures commonly used to describe population in more detail.


  1. Median Age
    1. Read the median ages for 1980 and 1990 from the US County File. Subtract 1980 values from 1990 to determine the change in median age. Because the U.S. has a low birthrate, the national population is, on the average, getting older. It is not changing as rapidly as it would, however, without immigration, which tends to add younger people to the population. Immigrants also have a higher brith rate than U.S.-born people.
    2. Sort the 1990 data to determine which counties have the oldest and youngest populations. Create a map of this data to see if there are any regional patterns in it. What parts of the U.S. have the oldest populations and what parts have the youngest? Why do these patterns exist?
    3. Sort the 1980-1990 differences and determine which counties experienced the largest change in median age. Can you offer any explanation for the changes? Because the key influences on patterns and trends of aging are the birthrate and migration flows into and out of places, your explanations will probably involve speculation on the characteristics of local populations that may relate to birthrate and migration.
  2. Percentages of Total Population
    1. Read the age data for Burbank and Glendale tracts. Compute the percent of the total population under age 15 and the percent of the population over age 64 for all tracts in either Burbank or Glendale as well as for the city as a whole. Select the tract with the highest percent under 15 and the tract with the highest percent over age 64 and compare them to the city percentages. How different are they? In larger cities, what factors might make some tracts much younger and others much older than the city as a whole?
  3. Age Dependency Ratios
    1. Calculate the Elderly Dependency Ratio for either the city of Burbank or the city of Glendale. Calculate the Youth Dependency Ratio for either the city of Burbank or the city of Glendale. Which is greater -  the Elderly or the Youth Dependency Ratio? The rationale behind the calculation of dependency ratios is that these age groups depend on the earnings and taxes generated by the working ages, 15 - 64.
  4. Population Pyramid
    1. Read the age data for Burbank and Glendale tracts. Calculate the percentages of males and females in each age category for the entire city of Burbank or the entire city of Glendale. Select one or two tracts within the same city and compute the same set of age group percentages.
    2. Using a graphing program assign a negative value to the male data and enter the male and female values as two series. Describe in a sentence the age breakdown of males and females for the tract compared to the city as a whole. Comparing the tract difference in age-sex structure with the city as a whole, what do you think is different in this tract that would produce this different age-sex structure?

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