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Data Dictionary: ACS 2008 (3-Year Estimates)
you are here: choose a survey survey data set table variable details
Data Source: Social Explorer; U.S. Census Bureau
Universe: Total Population
Variable Details
T9. Median Age by Sex
Universe: Total Population
T009_001Median Age:
Percent base:
None - percentages not computed
Aggregation method:
Median, using bracket table: T200, interpolation method: Linear
Formula used to compute this variable:
Return_Value = ACS08_3yr:B01002001; if (ACS08_3yr:B01002001.IsNull) Return_Value.IsNull = true
Variables used in the formula:
ACS08_3yr:B01002001
Median Age -- Total
Relevant Documentation:
Excerpt from: Social Explorer; U.S. Census Bureau; American Community Survey 2006-2008 Summary File: Technical Documentation.
  ACS 2008-3yr Summary File: Technical Documentation -> Appendix B: Subject Definitions -> Population Variables -> Age -> Median Age
Median Age
The median age is the age that divides the population into two equal-size groups. Half of the population is older than the median age and half is younger. Median age is based on a standard distribution of the population by single years of age and is shown to the nearest tenth of a year. (See the sections on "Standard Distributions" and "Medians" under "Derived Measures.")
Excerpt from: Social Explorer; U.S. Census Bureau; American Community Survey 2006-2008 Summary File: Technical Documentation.
  ACS 2008-3yr Summary File: Technical Documentation -> Appendix B: Subject Definitions -> Population Variables -> Sex
Sex
The data on sex were derived from answers to Question 3. Individuals were asked to mark either "male" or "female" to indicate their sex. For most cases in which sex was not reported, the appropriate entry was determined from the persons given (i.e., first) name and household relationship. Otherwise, sex was imputed according to the relationship to the householder and the age of the person.
Sex Ratio
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The sex ratio represents the balance between the male and female populations. Ratios above 100 indicate a larger male population, and ratios below 100 indicate a larger female population. This measure is derived by dividing the total number of males by the total number of females and then multiplying by 100. It is rounded to the nearest tenth.
Limitation of the data
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Beginning in 2006, the population in group quarters (GQ) is included in the ACS. Some types of GQ populations have sex distributions that are very different from the household population. The inclusion of the GQ population could therefore have a noticeable impact on the sex distribution. This is particularly true for areas with a substantial GQ population.

The Census Bureau tested the changes introduced to the 2008 version of the sex question in the 2007 ACS Grid-Sequential Test (http://www.census.gov/acs/www/Downloads/ACS-MP-09_Grid-Sequential_Test_Final_Report.pdf).

The results of this testing show that the changes may introduce an inconsistency in the data produced for this question as observed from the years 2007 to 2008
Question/Concept History
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Beginning in 2008, the layout of the sex question response categories was changed to a horizontal side-by-side layout from a vertically stacked layout on the mail paper ACS questionnaire.