The 2010 Decennial Census

Things You Need to Know

• There is no long form this time. Previous decennial censuses had two different questionnaires: a "short form" with a relatively small number of questions, which everybody had to answer; and a "long form" with many more questions, which was sent to a sample (about one in six) of households. The long form asked questions regarding your income, education, occupation, how and where you travel to work, if you have any disabilities, etc. This was sometimes referred to by veteran statisticians and journalists as "the good stuff". Since there is no long form in 2010, we cannot expect to get any data products containing any of this "good stuff". This means that there was not a Summary File 3 (SF3) this time. (Nor an SF4, etc.)
• Why not? Because while the good stuff was very good, it became less good as the decade following each census went on. It got a little old. So, for example, by the time we got new 2000-census SF3 data in 2002 the SF3 data from 1990 was 12 years old. It was decided that what was needed was a new "continous measurement" approach, which would involve doing a survey with a questionnaire similar to the decennial census long form that would be administered to a sample of the population througout the decade. This idea was implemented as the American Community Survey (ACS). To get congressional support for the ACS, the Bureau had to promise that they would recover some of the ACS cost by not doing a long form in the decennial census any more. What this means is that if you are looking for poverty rates for census tracts in Cincinnati (for example) then you have come to the wrong place. Poverty data are based on questions regarding people's income; these were long-form questions. The published data — based upon questions that only appeared on the long form, which was only administered to a sample of the population — was referred to as sample data. So, there is no sample data to be found here in the 2010 decennial census section. For that sort of information, you'll need to go to the American Community Survey section.
• There is an important (but complex) link between the decennial and ACS data. In a certain sense, the decennial censuses of past decades could be looked at as two separate surveys: the short-form-only survey and the long-form survey. But they were very closely tied and the sampling issues invovled in processing the long-form data were relatively simple, since the short form data allowed the Bureau to know exactly not only the households (and group quarters) that were sampled, but also how large the sampling universes were. Although there were differences in the basic counts for a census tract reported on SF1 (short-form data) vs. SF3 (long-form or sample data), the differences were rarely nontrivial. There was a single common sampling universe based on a single point in time (April 1 of the decennial census year) and shared rules regarding residency and other fine points of where (e.g., where to count college students and snowbirds) and how much to count the data (weighting, based on sampling factors). Most of that straightforward linkage and consistency is gone now. The relationship of the decennial data and the ACS data is only vaguely understood by everyone but a handful of statisticians who really comprehend the Census Bureau's complex use of controls and weighting to produce ACS data estimates. An oversimplified summary: The ACS uses population "controls" to complete their estimation process. Those controls are based on the post-censal population estimates by age, race, sex, and hispanic origin for the survey period, and those estimates are based to a considerable extent on the most recent census counts.
• Why use census data if the ACS contains all the "good stuff"? If you need data for very small geographic areas, such as census blocks or block groups, small cities or townships, etc. then the decennial data may be your only viable source. Block data are not available from the ACS, and block group data are very limited; not to mention that they are based on five-year periods, usually come with large degrees of sampling error, and (in the case of block groups) are not available via the MCDC's ACS Profiles app. So, if you want to know how many children or senior citizens live in a neighborhood, you are going to have to go with the decennial data (even when it starts aging over the decade). Decennial data (when available) are better, because they are actual counts rather than sample estimates. Although you can use the ACS to get updated population data for entities as small as block groups through the decade, these will be statistical estimates based on a varying and sometimes inadequate sample size.

MCDC Data Holdings

You will need to know how to use Uexplore/Dexter to access our data holdings. The MCDC offers a complete set of SF1 data sets for the entire country. We have the SF1A series data for each state, the revised versions that include the updated urban/rural definitions. We have both the original complete table data (in the sf12010 data directory) and our standard extracts based on those table (in the sf12010x directory). We also have the SF1C files with higher-level geographies for the entire country.

To access any of the data collections we have per the 2010 census using the MCDC's Uexplore/Dexter application, go to the Decennial Census 2010 section of the Uexplore directory page, where you will find links to the relevant data directories. We have data from SF2 and PL94 in addition to the SF1 data.

MCDC Custom Applications

The MCDC has two special web applications that provide enhanced and easier access to the SF1 data for 2010.

• The 2010 Census SF1 Profile application allows you to select any geographic areas (up to four at one time) in the country and display a report featuring the most frequently requested data items from the SF1 standard extract data sets. See a sample report.
• For users who want their data for more than four geographic areas at a time and perhaps in a format more suitable for mapping and statistical analyis, the MCDC offers the SF1 Data extract app. This is a custom front end to the Dexter application that lets you make choices of the geographic areas (entire U.S. or selected states and/or counties) and geographic units (summary levels). For example, you can easily specify that you would like to see block- or block-group-level data for any state or states in the U.S.