Sample characteristics: United States

Census characteristics
  1960 1970 1980 1990 2000 2005 2010
Title 1960 Census of Population and Housing 1970 Census of Population and Housing 1980 Census of Population and Housing 1990 Census of Population and Housing 2000 Census of Population and Housing 2005 American Community Survey 2010 American Community Survey
Census agency U.S. Census Bureau U.S. Census Bureau U.S. Census Bureau U.S. Census Bureau U.S. Census Bureau U.S. Census Bureau U.S. Census Bureau
Population universe Residents of the 50 states (not the outlying areas). Residents of the 50 states (not the outlying areas). Residents of the 50 states (not the outlying areas). Residents of the 50 states (not the outlying areas). Residents of the 50 states (not the outlying areas). Residents of the 50 states (not the outlying areas) and Puerto Rico living in their residence for at least two months, excluding populations living in group quarters. Residents of the 50 states (not the outlying areas).
De jure or de facto De jure De jure De jure De jure De jure De jure De jure
Enumeration unit Households and Group Quarters Households and Group Quarters Households and Group Quarters Households and Group Quarters Households and Group Quarters Households Households and Group Quarters
Census day April 1, 1960 April 1, 1970 April 1, 1980 April 1, 1990 April 1, 2000 No specific day No specific day
Enumeration forms The 1960 census used a machine-readable household form. Separate forms were used for each housing unit. Housing questions were included on the same form as the population items. Every fourth enumeration unit received a "long form," containing supplemental sample questions that were asked of all members of the unit. Sample questions are available for all individuals in every unit. Of the units receiving a long form, four-fifths received one version (the 20% questionnaire), and one-fifth received a second version with the same population questions but slightly different housing questions (the 5% questionnaire). One in five housing units in 1970 received a long form containing supplemental sample questions. There were two versions of the long form, with different inquiries on both housing and population items; 15 percent of households received one version, and 5 percent received the other. Six independent 1 percent public use samples were produced for 1970, three from the 15 percent questionnaire and three from the 5 percent questionnaire. IPUMS-International uses the "Form 2 Metro" sample. The 1980 census employed a single long form questionnaire completed by one-half of housing units in places with a population under 2,500 and one-sixth of other housing units. The 1990 census used a single long-form questionnaire completed by one-half of persons in places with a population under 2,500, one-sixth of persons in other tracts and block numbering areas with fewer than 2,000 housing units, and one-eighth of all other areas. Overall, about one-sixth of housing units completed a long form. The 2000 census used a long form questionnaire. Long Form Sampling Entities (LFSEs) were used to determine sampling rates. If the smallest LFSE that included all or any part of a block had an estimated housing unit count of less than 800, the housing units in the block were sampled at a 1-in-2 rate. If it had an estimated housing unit count of 800 or more but less than 1,200, units were sampled at a 1-in-4 rate. If a block was not in either of the two previous categories, and was part of an interim census tract with 2,000 or more estimated housing units, units were sampled at a 1-in-8 rate. Housing units in all remaining blocks were sampled at a 1-in-6 rate. When all sampling rates were taken into account across the nation, approximately 1 out of every 6 housing units was included in the Census 2000 sample. The 2005 American Community Survey employed a single long form questionnaire completed by one of 100 households. The 2010 American Community Survey employed a single long form questionnaire completed by one of 100 households and group quarters.
Type of fieldwork Direct and self-enumeration Direct and self-enumeration Direct and self-enumeration Direct and self-enumeration Direct and self-enumeration Direct and self-enumeration Direct and self-enumeration
Respondent Not specified Not specified Not specified Not specified Not specified Not specified Not specified
Undercount No official estimates No official estimates No official estimates No official estimates No official estimates No official estimates No official estimates

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Microdata sample characteristics
  1960 1970 1980 1990 2000 2005 2010
Microdata source U.S. Census Bureau U.S. Census Bureau U.S. Census Bureau U.S. Census Bureau U.S. Census Bureau U.S. Census Bureau U.S. Census Bureau
Sample unit Household Household Household Household Household Household Household
Sample fraction 1% 1% 5% 5% 5% 1% 1%
Sample size (person records) 1,799,888 2,029,666 11,343,120 12,501,046 14,081,466 2,878,380 3,061,692
Sample weights Self-weighting.

Expansion factor = 100.
Self-weighting.

Expansion factor = 100.
Self-weighting.

Expansion factor = 100.
Weights computed by census agency should be used for most types of analysis. Weights computed by census agency should be used for most types of analysis. Weights computed by census agency should be used for most types of analysis. Weights computed by census agency should be used for most types of analysis.

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Units identified
  1960 1970 1980 1990 2000 2005 2010
Dwellings No No No No No No No
Vacant units No Yes Yes Yes Yes Yes Yes
Smallest geography State Metropolitan areas and county groups with 250,000+ residents PUMAS (Public Use Microdata Areas (PUMAs) containing 100,000 or more residents PUMAS (Public Use Microdata Areas (PUMAs) containing 100,000 or more residents PUMAS (Public Use Microdata Areas (PUMAs) containing 100,000 or more residents PUMAS (Public Use Microdata Areas (PUMAs) containing 100,000 or more residents PUMAS (Public Use Microdata Areas (PUMAs) containing 100,000 or more residents
Households Yes Yes Yes Yes Yes Yes Yes
Individuals Yes Yes Yes Yes Yes Yes Yes
Group quarters Yes Yes Yes Yes Yes No Yes

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Unit definitions
  1960 1970 1980 1990 2000 2005 2010
Households Dwelling places with fewer than five persons unrelated to a household head, excluding institutions and transient quarters. Dwelling places with fewer than five persons unrelated to a household head, excluding institutions and transient quarters. Dwelling places with fewer than ten persons unrelated to a household head, excluding institutions and transient quarters. Dwelling places with fewer than ten persons unrelated to a household head, excluding institutions and transient quarters. Dwelling places excluding institutions and transient quarters. Dwelling places excluding institutions and transient quarters. Dwelling places excluding institutions and transient quarters.
Group quarters Institutions, transient quarters, and dwelling places with five or more persons unrelated to a household head. Institutions, transient quarters, and dwelling places with five or more persons unrelated to a household head. Institutions, transient quarters, and dwelling places with ten or more persons unrelated to a household head. Institutions, transient quarters, and dwelling places with ten or more persons unrelated to a household head. No threshold was applied; in order for a household to be considered group quarters in 2000, it had to be on the list of group quarters that is continuously maintained by the Census Bureau. Not included in microdata sample. A place where people live or stay, in a group living arrangement, that is owned or managed by an entity or organization providing housing and/or services for the residents. These services may include custodial or medical care as well as other types of assistance, and residency in commonly restricted to those receiving these services. People living in group quarters are usually not related to each other. Group quarters inlcude such places as college residence halls, residential treatment centers, skilled nursing facilities, group homes, military barracks, correctional facilities, and workers' dormitories.

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