The significance of age and sex data

In general, the U.S. population continues to grow older with a median age over 40 years old in many states. At the same time, increases in the number of men at older ages are apparent. Understanding a population’s age and sex composition yields insights into changing phenomena and highlights future social and economic challenges.

For the most recent decennial census, age was the length of time in completed years that a person had lived as of Census Day--April 1, 2010. The Census Bureau’s national surveys compute age as of the interview date.

Data on age and sex are available from a number of sources including the decennial census, the American Community Survey, and the Current Population Survey. The Population Estimates Program provides current and historical official population estimates by age, sex, race, and Hispanic origin for the nation, states, and counties.

  • Data by age and sex can be obtained from American Factfinder (AFF) and decennial census printed reports which have been scanned from the printed census reports and posted on-line.
  • 2012 National Projections provide age, sex, race, and Hispanic origin from 2012 out to 2060. The Summary Tables provide age by selected age groups; the Downloadable Files provide single year of age and sex.
  • Historical population estimates by age and sex can be obtained from our Archives. These are available for the 2000s, 1990s, 1980s, and pre-1980s for the nation, states, and counties. Pre-1980 data for the nation provide age and sex from 1900 to 1999, and pre-1980 data for states provide age and sex for 1970 to 1980.
  • State Projections from 2000 to 2030 are available for age and sex only. The Summary Tables and Detailed Data Files provide the same breakdowns for states.
  • The Census Bureau's International Data Base provides national-level population estimates and projections by age and sex for all other countries of the world.
Distinction between the concepts of gender and sex

In general discussions, the concept of gender is often confused with the concept of sex, and the terms are used interchangeably. The meanings of these two concepts are not the same: sex is based on the biological attributes of men and women (chromosomes, anatomy, hormones), while gender is a social construction whereby a society or culture assigns certain tendencies or behaviors to the labels of masculine or feminine. These assignments may differ across cultures and among people within a culture, and even across time. Gender may or may not correspond directly to sex--depending on the society or culture or period. That means, for example, that people may associate themselves with femininity (as defined by their culture) while being biologically male. At the Census Bureau, the sex question wording very specifically intends to capture a person's biological sex and not gender. Ambiguity of these two concepts interferes with accurately and consistently measuring what we intend to measure--the sex composition of the population.

Purpose of the two-part question, “What is your age and what is your date of birth?”

The purpose of this two-part question frequently used in Census Bureau questionnaires is to ensure accuracy of age data and to minimize non-response rates. Because age is a critical element in determining federal funding, it is imperative to have high quality age data. Age is also a basic demographic characteristic that is crossed by social characteristics, such as marital status and education, and economic characteristics, such as labor force participation and poverty, in many data products. Especially because of the multiple uses of age data and their visibility, it is important that they be of high quality. Asking for both date of birth in month, day, and year format, along with age, helps to ensure that quality.

More detailed data are available…
…by single years of age
…on the older population
  • Decennial Census: Demographic Profile and Summary File 1 data, printed reports
  • ACS: Subject table data
  • CPS: Tables
Contact Us

For assistance, please contact the Census Call Center at 1-800-923-8282 (toll free) or visit ask.census.gov for further information.