Population Pyramids
M. Richmond
Demography
The study of the characteristics of population (from Greek root demos
meaning people and graphos to make a line) can be complex. Population
pyramids are a useful tool for understanding the structure and composition of
populations because they graphically portray many aspects of a population,
such as sex ratios and age structure (Fig. 82).
In the pyramid, the percent of females is displayed to the left, and the males to the
right. While slightly more males are born in any given population, the number of
females surviving to older ages is greater than the number of surviving males.
Age cohorts are listed
down the center of the
pyramid, and are
divided into five-year
increments.
Female Male
85+
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
16%
14%
12%
10%
8%
6%
4%
2%
0%
2%
4%
6%
8%
10%
12%
14%
1970, and 1990. These times have been chosen to help illustrate the change
in the structure of American society. They bracket important transitions in
demographic factors through time. Some of the bar widths in the pyramids
for 1930 were adjusted to reflect the difference in how the data were collected for that year. The thicker bars represent age cohorts that are divided
into larger increments than the standard five-year increments shown in both
1970 and 1990.
Portions of all WRB counties except Linn and Marion lie outside of the
basin. For these counties, adjustment has not been made in the pyramids to
reflect the portion of their populations that reside within the basin, and because populations are distributed unevenly across a county, this may affect
the results. Also, note that the size of the pyramids does not account for differences in population size between the counties, which can vary considerably. This information for 1990 is summarized in Figure 84.
16%
Percent of Population
Figure 82. Anatomy of a population pyramid. The “percent of population” is calculated by the number of people of one gender in one age
cohort relative to the total number of people of that gender in the population. Summing the bars on both sides of the graph would yield the
percent of one age cohort.
Female Male
Female Male
Percent of Population
Percent of Population
Expansive
Constrictive
Female Male
Percent of Population
Stationary
Figure 83. Population pyramid types. Demographers recognize three
prototypical pyramid structures, constrictive, expansive, and stationary.
All indicate conditions of the populations which comprise them. A constrictive pyramid has fewer people in the younger age categories, and has
been typical of U.S. populations as baby boom populations shift to more
conservative birth rates. An expansive pyramid represents greater numbers of people in the younger age categories, and is typical of many
developing countries where birth rates are high, but conditions are harsh,
and life expectancy is short. A stationary pyramid shows roughly equal
numbers of people in all age categories, with a tapering towards the
older age categories. Countries such as Sweden show stationary age
categories because of relatively low, constant birth rates, and a high
quality of life.73
1930
Female Male
85+
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
Percent of Population
Given these considerations, at least three distinct forms can be seen in
the population pyramids of 1990 for the counties which intersect the WRB.
In Lincoln and Tillamook counties, which are predominantly outside of the
WRB, a double hour-glass form is apparent, attributable to the above mentioned baby boom and echo cohorts common to the United States as a whole.
A third, large, older cohort, attracted to these areas because of their retirement amenities,72 is also apparent. Benton County shows a predominance of
people in the low to mid-twenties attending Oregon State University (OSU).
For comparison, consider Lane County with the University of Oregon. The
large student population is less apparent because of Lane County’s larger
overall population and more urban context. Most other counties fall into a
third, generally constrictive pyramid, indicating smaller numbers of people
30
in the younger ages.
Most of the pyramids for the counties that intersect the WRB depict an
interesting phenomenon in the change of late survivorship over time. It is apparent that in 1930 the age cohort of 75 and over is dominated by the male
population. In 1990 the late survivorship of the female population becomes
substantially greater than that of the males. This phenomenon is illustrated
for Lane County in Figure 85. The purple path shows this pattern of late survivorship while the green path traces the 20-24 age cohort of 1930 through
time to the 80-84 age cohort of 1990. One can apply this simple analysis to
any of the other counties using the population pyramids on the facing page.
1970
Female Male
85+
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
Percent of Population
8%
1990
Percent of Population
The pyramids in Map 15 are based on the total population of the counties which intersect the area of the Willamette River Basin (WRB) in 1930,
Figure 84. 1990 county population by gender and total.
Female Male
85+
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
Percent of Population
64
PNW Ecosystem Research Consortium
6.49
6%
5%
4%
4.18
3.77
3%
2.73
2%
1%
.62
.73
1930
>75yr
1970
>75yr
1990
>75yr
10%
female
male
9.81
8%
9.33
6%
4%
3.75
3.80
2%
1.93
1.26
0%
Figure 85. Lane County population pyramids for 1930, 1970, and 1990, and gender ratios for the trajectories
female
male
7%
0%
Percent of Population
Pyramids can give insight into trends in population over time by their
portrayal of the relative number of people in a particular cohort. For example, the swell of population in the “baby boom” cohort, now in its forties
and fifties, is apparent in many of the county population pyramids, as is the
“echo” baby boom, now five to fifteen years of age. Demographers have divided population pyramids into three prototypical types (Fig. 83). While
these prototypes are useful for general interpretation of conditions, knowledge of specific characteristics of particular populations is also important as
they may significantly contribute to differences between counties.
1930
20-24yr
1970
60-64yr
1990
80-84yr
HUMAN POPULATION
Map 15. Population Pyramids
74
Female Male
85+
80-84
75-79
70-74
65-69
60-64
55-59
50-54
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
Percent of Population
Counties
1970
1930
Female
Benton
16%
14%
12%
10%
8%
6%
4%
2%
Male
Female Male
Female Male
85 +
85 +
85 +
80-84
80-84
80-84
75-79
75-79
75-79
70-74
70-74
70-74
65-69
65-69
65-69
60-64
60-64
60-64
55-59
55-59
55-59
50-54
50-54
50-54
45-49
45-49
45-49
40-44
40-44
40-44
35-39
35-39
35-39
30-34
30-34
30-34
25-29
25-29
25-29
20-24
20-24
20-24
15-19
15-19
15-19
10-14
10-14
5-9
5-9
0-4
0-4
0%
Female
Clackamas
16%
14%
12%
10%
8%
6%
4%
2%
2%
16%
14%
12%
10%
8%
6%
4%
2%
16%
14%
12%
10%
8%
6%
4%
2%
16%
14%
12%
10%
8%
6%
4%
2%
14%
12%
10%
8%
6%
4%
14%
12%
10%
8%
6%
4%
14%
12%
10%
8%
6%
4%
12%
10%
8%
6%
4%
2%
0%
10-14
5-9
0-4
2%
4%
6%
8%
10%
12%
14%
16%
16%
14%
12%
10%
8%
6%
4%
2%
80-84
75-79
70-74
65-69
60-64
60-64
60-64
55-59
55-59
55-59
50-54
50-54
50-54
45-49
45-49
45-49
40-44
40-44
40-44
35-39
35-39
35-39
30-34
30-34
30-34
25-29
25-29
25-29
20-24
20-24
20-24
15-19
15-19
10-14
10-14
5-9
5-9
0-4
0-4
0%
2%
4%
6%
8%
10%
12%
14%
16%
16%
14%
12%
10%
8%
6%
4%
2%
Male
0%
10%
12%
14%
16%
16%
14%
12%
10%
8%
6%
4%
2%
0%
85 +
85 +
80-84
80-84
75-79
75-79
70-74
70-74
65-69
65-69
60-64
60-64
60-64
55-59
55-59
55-59
50-54
50-54
50-54
45-49
45-49
45-49
40-44
40-44
40-44
35-39
35-39
35-39
30-34
30-34
30-34
25-29
25-29
25-29
20-24
20-24
20-24
15-19
15-19
10-14
10-14
5-9
5-9
0-4
0-4
10%
12%
14%
16%
16%
14%
12%
10%
8%
6%
4%
2%
0%
10%
12%
14%
16%
16%
14%
12%
10%
8%
6%
4%
2%
0%
85 +
80-84
80-84
75-79
75-79
70-74
70-74
65-69
65-69
60-64
60-64
60-64
55-59
55-59
55-59
50-54
50-54
50-54
45-49
45-49
45-49
40-44
40-44
40-44
35-39
35-39
35-39
30-34
30-34
30-34
25-29
25-29
25-29
20-24
20-24
20-24
15-19
15-19
10-14
10-14
5-9
5-9
0-4
0-4
8%
10%
12%
14%
16%
16%
14%
12%
10%
8%
6%
4%
2%
Male
0%
10%
12%
14%
16%
16%
14%
12%
10%
8%
6%
4%
2%
85 +
80-84
80-84
75-79
75-79
70-74
70-74
65-69
65-69
60-64
60-64
60-64
55-59
55-59
55-59
50-54
50-54
50-54
45-49
45-49
45-49
40-44
40-44
40-44
35-39
35-39
35-39
30-34
30-34
30-34
25-29
25-29
25-29
20-24
20-24
20-24
15-19
15-19
10-14
10-14
5-9
5-9
0-4
0-4
12%
14%
16%
16%
14%
12%
10%
8%
6%
4%
2%
0%
85 +
85 +
80-84
80-84
75-79
75-79
70-74
70-74
65-69
65-69
60-64
60-64
55-59
55-59
50-54
50-54
45-49
45-49
40-44
40-44
35-39
35-39
30-34
30-34
25-29
25-29
20-24
20-24
15-19
15-19
10-14
10-14
5-9
5-9
0-4
0-4
2%
12%
10%
8%
6%
4%
4%
6%
8%
10%
12%
14%
16%
16%
14%
12%
10%
8%
6%
4%
2%
10%
12%
14%
16%
16%
14%
12%
10%
8%
6%
4%
2%
Polk
16%
14%
12%
10%
8%
6%
4%
0%
Tillamook
16%
14%
12%
10%
8%
6%
4%
16%
14%
12%
10%
8%
6%
4%
14%
16%
2%
4%
6%
8%
10%
12%
14%
16%
0%
2%
4%
6%
8%
10%
12%
14%
16%
2%
4%
6%
8%
10%
12%
14%
16%
2%
4%
6%
8%
10%
12%
14%
16%
2%
4%
6%
8%
10%
12%
14%
16%
45-49
40-44
35-39
30-34
25-29
20-24
15-19
10-14
5-9
0-4
2%
4%
6%
8%
10%
12%
14%
16%
16%
14%
12%
10%
8%
6%
4%
2%
0%
Female Male
85 +
80-84
75-79
70-74
65-69
60-64
55-59
55-59
55-59
50-54
50-54
50-54
45-49
45-49
45-49
40-44
40-44
40-44
35-39
35-39
35-39
30-34
30-34
30-34
25-29
25-29
25-29
20-24
20-24
20-24
15-19
15-19
10-14
10-14
5-9
5-9
0-4
0-4
2%
4%
6%
8%
10%
12%
14%
16%
16%
14%
12%
10%
8%
6%
4%
2%
0%
15-19
10-14
5-9
0-4
2%
4%
6%
8%
10%
12%
14%
16%
16%
14%
12%
10%
8%
6%
4%
0%
2%
Female Male
Male
Female Male
85 +
85 +
85 +
80-84
80-84
80-84
75-79
75-79
75-79
70-74
70-74
70-74
65-69
65-69
65-69
60-64
60-64
60-64
55-59
55-59
55-59
50-54
50-54
50-54
45-49
45-49
45-49
40-44
40-44
40-44
35-39
35-39
35-39
30-34
30-34
30-34
25-29
25-29
25-29
20-24
20-24
20-24
15-19
15-19
15-19
10-14
10-14
5-9
5-9
0-4
0-4
2%
4%
6%
8%
10%
12%
14%
16%
16%
14%
12%
10%
8%
6%
4%
2%
0%
10-14
5-9
0-4
2%
4%
6%
8%
10%
12%
14%
16%
16%
14%
12%
10%
8%
6%
4%
2%
Female Male
Male
0%
Female Male
85 +
85 +
80-84
80-84
75-79
75-79
70-74
70-74
65-69
65-69
65-69
60-64
60-64
60-64
55-59
55-59
55-59
50-54
50-54
50-54
45-49
45-49
45-49
40-44
40-44
40-44
35-39
35-39
35-39
30-34
30-34
30-34
25-29
25-29
25-29
20-24
20-24
20-24
15-19
15-19
10-14
10-14
5-9
5-9
0-4
0-4
85 +
80-84
75-79
70-74
2%
4%
6%
8%
10%
12%
14%
16%
16%
14%
12%
10%
8%
6%
4%
2%
0%
15-19
10-14
5-9
0-4
2%
4%
6%
8%
10%
12%
14%
16%
16%
14%
12%
10%
8%
6%
4%
2%
Female Male
Male
0%
Female Male
85 +
85 +
85 +
80-84
80-84
80-84
75-79
75-79
75-79
70-74
70-74
70-74
65-69
65-69
65-69
60-64
60-64
60-64
55-59
55-59
55-59
50-54
50-54
50-54
45-49
45-49
45-49
40-44
40-44
40-44
35-39
35-39
35-39
30-34
30-34
30-34
25-29
25-29
25-29
20-24
20-24
20-24
15-19
15-19
10-14
10-14
5-9
5-9
0-4
0-4
2%
4%
6%
8%
10%
12%
14%
16%
16%
14%
12%
10%
8%
6%
4%
2%
0%
15-19
10-14
5-9
0-4
2%
4%
6%
8%
10%
12%
14%
16%
16%
14%
12%
10%
8%
6%
4%
2%
0%
Female Male
Male
85 +
85 +
80-84
80-84
75-79
75-79
75-79
70-74
70-74
70-74
65-69
65-69
65-69
60-64
60-64
60-64
55-59
55-59
55-59
50-54
50-54
50-54
45-49
45-49
45-49
40-44
40-44
40-44
35-39
35-39
35-39
30-34
30-34
30-34
25-29
25-29
25-29
20-24
20-24
20-24
15-19
15-19
10-14
10-14
5-9
5-9
0-4
0-4
2%
4%
6%
8%
10%
12%
14%
16%
16%
14%
12%
10%
8%
6%
4%
2%
0%
10%
12%
14%
16%
16%
14%
12%
10%
8%
6%
4%
2%
0%
85 +
85 +
80-84
80-84
75-79
75-79
70-74
70-74
65-69
65-69
65-69
60-64
60-64
60-64
55-59
55-59
55-59
50-54
50-54
50-54
45-49
45-49
45-49
40-44
40-44
40-44
35-39
35-39
35-39
30-34
30-34
30-34
25-29
25-29
25-29
20-24
20-24
20-24
15-19
15-19
10-14
10-14
5-9
5-9
0-4
0-4
10%
12%
14%
16%
16%
14%
12%
10%
8%
6%
4%
2%
Male
0%
10%
12%
14%
16%
16%
14%
12%
10%
8%
6%
4%
2%
Female Male
0%
85 +
80-84
75-79
75-79
70-74
70-74
65-69
65-69
65-69
60-64
60-64
60-64
55-59
55-59
55-59
50-54
50-54
50-54
45-49
45-49
45-49
40-44
40-44
40-44
35-39
35-39
35-39
30-34
30-34
30-34
25-29
25-29
25-29
20-24
20-24
20-24
15-19
15-19
10-14
10-14
5-9
5-9
0-4
0-4
6%
4%
2%
0%
6%
8%
10%
2%
4%
6%
8%
10%
2%
4%
12%
14%
16%
12%
14%
16%
Female Male
85 +
80-84
8%
4%
0-4
8%
85 +
10%
2%
5-9
6%
70-74
12%
16%
15-19
4%
75-79
14%
14%
10-14
2%
80-84
16%
12%
Female Male
85 +
8%
10%
0-4
8%
70-74
6%
8%
5-9
6%
75-79
4%
6%
10-14
4%
80-84
2%
4%
15-19
2%
Female Male
Male
2%
Female Male
85 +
80-84
Female
Yamhill
12%
50-54
60-64
0%
10%
55-59
65-69
2%
8%
60-64
60-64
Female
Washington
6%
65-69
65-69
0%
4%
70-74
85 +
2%
2%
75-79
70-74
Female
16%
80-84
75-79
0%
14%
85 +
80-84
2%
12%
Female Male
Female Male
Male
Female
Polk
10%
0-4
8%
85 +
0%
8%
5-9
6%
70-74
2%
6%
10-14
4%
75-79
0%
4%
15-19
2%
80-84
0%
2%
Female Male
Male
0%
16%
Female Male
85 +
85 +
Multnomah
14%
0%
65-69
10%
14%
0-4
8%
70-74
8%
12%
5-9
6%
75-79
6%
10%
10-14
4%
80-84
4%
8%
15-19
2%
Female Male
2%
6%
Female Male
85 +
85 +
65-69
6%
4%
0-4
8%
70-74
4%
2%
5-9
6%
75-79
2%
16%
10-14
4%
80-84
0%
14%
15-19
2%
Female Male
Male
12%
Female Male
85 +
65-69
8%
10%
0-4
8%
70-74
6%
8%
5-9
6%
75-79
4%
6%
10-14
4%
Female Male
2%
4%
15-19
2%
80-84
0%
2%
Female Male
85 +
85+
Female
16%
0%
Female Male
65-69
2%
Multnomah
14%
70-74
Female
16%
16%
75-79
2%
Marion
16%
80-84
Female
16%
14%
85 +
2%
Linn
12%
65-69
Female
16%
10%
70-74
0%
Lincoln
8%
75-79
Female
Lane
6%
80-84
Female
Douglas
4%
Male
Female
Columbia
1990
N
15-19
10-14
5-9
0-4
2%
4%
6%
8%
10%
12%
14%
16%
16%
14%
12%
10%
8%
6%
4%
2%
0%
6%
8%
10%
12%
14%
16%
S
Approximate Scale 1: 800000
Willamette River Basin Atlas
2nd Edition
65