older. To a young person, a birthday might mean an
opportunity to get a driver’s license or to vote for the
first time. To an older person, it might mean a retirement
party. Many health issues, from childhood diseases
to geriatric conditions, are associated with age.
These and many other life experiences are somewhat
different for the male population than for the female
population. The U.S. Census Bureau’s Population
Estimates Program produces age and sex data for the
United States, states, and counties.
Men and Women
Within the total resident population in 2005, women
and girls outnumbered men and boys by 4.4 million—
150.4 million compared with 146.0 million. This difference
was not spread evenly throughout the age
groups, as illustrated in the age pyramid shown in
Figure 1. Among those under 18, boys outnumbered
girls in 2005. From about age 40 on, women were the
majority. Among people in their nineties, the ratio of
men to women was 38 to 100, reflecting the greater
life expectancy of women than men.1 The pyramid
bulges in the middle, indicating the large cohort
known as the Baby Boom Generation, who were aged
41 to 59 in 2005. Other irregularities in the pyramid
frequently reflect years with relatively high or low
Between Census Day (April 1, 2000) and July 1, 2005,
the population of most 5-year age groups grew. Five
age groups experienced declines, as illustrated in
The largest decline (7.5 percent) was among the population
aged 35 to 39, the age group that the Baby
Boom Generation has left. The fastest-growing population
was the population aged 55 to 59. This age group
grew about 29 percent as the oldest Baby Boomers
replaced the smaller cohort of people who were born
While the total population increased 5 percent
between 2000 and 2005, people in their seventies
declined by 2.2 percent. A “birth dearth” during the
late 1920s and early 1930s was largely responsible for
this decline. Other older groups saw increases. The
population aged 85 and older grew by 20 percent.
On July 1, 2005, the median age of the population was
36.2 years—older than the highest median age ever
recorded in a census (35.3 in Census 2000).
U.S. Census Bureau Population Profile of the United States: Dynamic Version 1 AGE AND SEX DISTRIBUTION IN 2005
Words That Count
An age pyramid is a horizontal bar graph, usually
showing the size of the male population on
the left and the female population on the right,
with age groupings beginning with the youngest
populations on the bottom and ending with the
oldest ones at the top (Figure 1).
Median age is the age at which half the population
is older and half is younger.
A birth cohort is a group of people born during
the same time period.
The Baby Boom Generation is the large cohort
of people born from 1946 to 1964.
1 The number of males per 100 females is called the sex ratio. To find out more about sex ratios, see the chapters on men and women and on the older population.
2 Population Profile of the United States: Dynamic Version U.S. Census Bureau Figure 1.
Population by Single Year of Age and Sex: 2005
Source: U.S. Census Bureau, Population Estimates Program, July 1, 2005. 0.0 0.5 1.0 1.5 2.0 2.5
2.5 2.0 1.5 1.0 0.5 0.0
Male population Age Female population
BABY BOOM GENERATION
U.S. Census Bureau Population Profile of the United States: Dynamic Version 3 Figure 2.
Percent Change in Population by Age: 2000 to 2005
Source: U.S. Census Bureau, Population Estimates Program, April 1, 2000, and July 1, 2005. 5.9
Under 5- 9 10-14 15-19 20-24 25-29 30-34 35-39 40-44 45-49 50-54 55-59 60-64 65-69 70-74 75-79 80-84 5