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PART I: Using the American Community Survey, 2 Essentials for Users
Pages 27-76

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From page 27...
... PART I Using the American Community Survey
From page 29...
... Finally, it offers the panel's assessment of the value of the ACS to users based on the available knowledge about its properties. 2-A ACS DESIGN BASICS To work with data from the ACS, users should be acquainted with the following features of its design and operations: the population or universe covered, rules for assigning people to a place of residence, questionnaire content and reference periods, sample size and design, data collection procedures, data products, and data-processing procedures to generate the products.
From page 30...
... Following the same basic design as the ACS, the initial sample size of the PRCS is 3,000 housing units each month or 36,000 housing units each year -- about 2.4 percent of the total of about 1.5 million residential addresses in Puerto Rico. Initial sampling rates for blocks vary by the estimate of occupied housing units in the governmental jurisdiction or census tract (see Table 2-3, Part A)
From page 31...
... However, some people may report a different residence: for example, people who live in a house or apartment in New York most of the year but reside in Florida in December through March should report Florida as their address if sampled for the ACS in Florida in the winter, whereas their Census Day address is in New York. 2-A.3 Content and Reference Periods The 2005 ACS includes about 55 questions for every person and 30 questions for every housing unit in the sample -- approximately the same content as in the 2000 census long-form sample.
From page 32...
... 0.5b Other noninstitutional group quarters Residence in the ACS and the 2000 Long-Form Sample Convent, monastery Group home Halfway home Hospice Job Corps center Migrant worker quarters Shelter, emergency shelter YMCA, YWCA, hostel Residence NOT in the ACS but in the 2000 Long-Form Sample Circus quarters Crews on merchant ships Domestic violence shelter Recreational vehicle in a campground Soup kitchen or mobile food van site Street location for the homeless aHousing units are separate living quarters with direct access from the outside or through a common hall (U.S. Census Bureau, 2006:D-17)
From page 33...
... A question on field of bachelor's degree will be tested in 2007 and may be added to the ACS beginning in 2009. 2-A.4 Sample Design and Size The ACS sends out questionnaires to about 250,000 housing unit addresses every month that have been sampled from the Census Bureau's Master Address File (MAF; see Chapter 4 for details of the sampling operation)
From page 34...
... Yes (short form) Relationship to household reference person (person 1)
From page 35...
... Housing Items Type of building/number of units in structure Yes Year building built Yes When household reference person (person 1) moved in Yes Number of acres on property (single-family or mobile Yes home)
From page 36...
... Tables 2-3a, 2-3b, and 2-3c provide initial annual and 5-year sampling rates for governmental units and census tracts of different popu
From page 37...
... Because the initial ACS sample size will be kept at approximately 3 million residential addresses per year, the initial sampling rates shown will be slightly reduced as the number of occupied housing units grows. Townships and other minor civil divisions are recognized for sampling purposes in 12 states where they are functioning governments: Connecticut, Maine, Massachusetts, Michigan, Minnesota, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Vermont, and Wisconsin.
From page 38...
... SOURCE: Adapted from U.S. Census Bureau (2006:Tables 4.1, 4.2)
From page 39...
... SOURCE: Adapted from U.S. Census Bureau (2006:Tables 4.1, 4.2)
From page 40...
... Census Bureau, 2006:7-9)
From page 41...
... .  eSee Table 2-3a for oversampling rates for blocks in small jurisdictions of fewer than 500 people, 500-2,000 people, and 2,000-3,000 people.
From page 42...
... Only a small percentage of records, which are never identified, are swapped. In addition to the various procedures that are implemented to protect confidentiality for the 1-year, 3-year, and 5-year period estimates, the Census Bureau will combine individual categories and even delete entire tabulations from 1-year and 3-year period products when the sampling errors are very large (see Chapter 4 for details)
From page 43...
... 2-A.7 Data Processing -- 1-Year Period Estimates The computer programs to generate the ACS 1-year period data products each summer operate on 12 months of data collected in the preceding calendar year. These data include all of the mailed-back, CATI, and CAPI responses that were received in January through December of that year (including additional information obtained by telephone for incompletely filled out mail questionnaires)
From page 44...
... For 1-year and 3-year periods, collapsed tables may be provided when categories in a detailed table are suppressed because the estimates do not meet minimum precision criteria. Similar to the tabulations in Summary File 3 from the 2000 long-form sample; 5-year period ACS estimates will also include tabulations of journey-to-work items for traffic analysis zones (one or more blocks, block groups, or census tracts)
From page 45...
... • ACS summary files for 1-year, 3-year, and 5-year period estimates (under develop ment) -- In response to users, the Census Bureau is developing an ACS product similar to Summary File 3 from the 2000 long-form sample.
From page 46...
... Census Bureau, February 21, 2007. Because of changes in population and geographic boundaries, the actual numbers of areas with estimates published may differ from the numbers shown.
From page 47...
... .3 2-A.7.b  Weighting The edited, filled-in data records for the 12 months in a calendar year are weighted in a series of steps to produce 1-year period estimates that represent the entire population. Chapter 5 provides a complete description of the nine steps in the weighting process for housing units and their members; four key steps (1, 3, 5, and 6)
From page 48...
... Throughout, the ACS data for a calendar year are processed as a whole and not month by month. The only exception to date is that for areas in states affected by Hurricane Katrina and Hurricane Rita, the Census Bureau issued two sets of 2005 data products in early June 2006 -- one set for January–August 2005 and the other set for September–December 2005, reflecting conditions before and after the hurricanes.4 2-A.8 Data Processing -- 3-Year and 5-Year Period Estimates The computer programs to produce 3-year period products use the fully processed records for the 3 preceding calendar years, containing 36 months' worth of responses; the programs to produce 5-year period products use the fully processed records for the 5 preceding calendar years, containing 60 months' worth of responses.
From page 49...
... Amounts for housing value and costs are also inflated to reflect the average value of the dollar for the most recent calendar year. While the Census Bureau has not worked out all of the details of the weighting for 3-year and 5-year period data products, the general procedure will be to remove the adjustments to the 1-year period weights for housing unit nonresponse and agreement with housing unit and population controls and to make new adjustments.
From page 50...
... The Census Bureau's data release schedule calls for each set of estimates to become available 8–10 months after all the data needed to produce the estimates are collected. Long-form-sample tabulations typically required 2 years or more after Census Day to become available.
From page 51...
... It included about 587,000 responses from a nationwide sample in 1,203 counties plus samples in 36 counties that were ACS test sites. By comparing the C2SS and the 2000 long-form sample, the Census Bureau was able to evaluate the relative quality to be expected from the ACS in terms of unit (household)
From page 52...
... Population coverage and unit and item response rates have also been higher in the ACS than in the Current Population Survey Annual Social and Economic Supplement (CPS ASEC) , which is the nation's premier household survey of income, participation in government programs, employment, and family relationships.6 In addition to examining basic quality measures, the Census Bureau also compared the distributions of responses to individual items for the C2SS and the long-form sample, which mainly identified consistencies be 6 Incomparing the ACS and the CPS ASEC, users should bear in mind the many differences between the two surveys (see Nelson, 2006, and Section 3-F.2)
From page 53...
... . The challenge for users is, with the help of methodologists, to understand enough of the extent and nature of sampling and nonsampling errors in survey estimates to assess the utility of the estimates for the user's purpose and identify possible strategies for ameliorating the effects of these errors on survey inferences.
From page 54...
... The ACS web site provides net coverage rates for men and women for states and the United States and for six race/ethnicity categories for the United States. These rates are the weighted ACS estimate for the year in question for the relevant demo 2-B.2.a  High Unit Response Rate in the C2SS The Census Bureau never expected that the mail response would be as high in the ACS as in the census, nor has it been: it was 56 percent in the C2SS compared with 71 percent in the 2000 long-form sample.
From page 55...
... . The numerator for unit response rates is the number of mail, CATI, and CAPI responses for the year in question, weighted to account for different initial sampling and CAPI subsampling rates.
From page 56...
... . 2-B.2.c  More Complete Item Response in the C2SS Imputation rates for questionnaire items -- that is, the percentage of item responses for households (for housing questions)
From page 57...
... 2-B.2.d  Greater Quality Control in the C2SS and the ACS For the C2SS the Census Bureau implemented quality assurance procedures that were not included in the 2000 long-form-sample procedures because of cost and timing constraints. These same procedures are being used in the ACS.
From page 58...
... . These results appear due in part to differences in wording and format of the race and ethnicity questions, which the Census Bureau is investigating (U.S.
From page 59...
... . The reason is that the Census Bureau does not impute an ancestry when none is reported, and the C2SS had more complete reporting of this item than the long-form sample: 88 percent of people reported at least one ancestry in the C2SS compared with only 81 percent in the 2000 long-form sample (U.S.
From page 60...
... In addition, the CPS uses a fixed reference period for reporting employment status (see Bureau of Labor Statistics and U.S. Census Bureau, 2002:Ch.
From page 61...
... and (2) the greater sampling error of the ACS estimates compared with the long-form-sample estimates (Section C.2)
From page 62...
... Such period estimates have lower sampling error than other types of estimates that could be constructed from the data, such as a middle-year estimate (see Chapter 6)
From page 63...
... It will update school district boundaries every 2 years and update the boundaries of statistical areas, including metropolitan areas, urbanized areas, PUMAs, census tracts, and block groups every decade in conjunction with the census. For ACS estimates for such governmental units as counties and cities, the Census Bureau will use the geographic boundaries as of January 1 of the most recent year of data that figure into the particular set of estimates.
From page 64...
... of the ACS 5-year period estimates would be about 20 percent greater than the errors of the long-form-sample estimates, but recent work (Starsinic, 2005) suggests that the ACS sampling errors will exceed the long-form-sample errors by about 50 percent.
From page 65...
... . 2-C.2.b  Illustrative, Approximate Sampling Error Estimates for the ACS The sampling error in an estimate may be measured by its standard error (see Box 2-5 for definitions of statistical terms)
From page 66...
... For the 2005 ACS, the Census Bureau directly estimated the sampling errors for specific estimates, including not only school-age poverty, but also other characteristics, using a repeated replication method (U.S. Census Bureau, 2006:Ch.12)
From page 67...
... To illustrate, consider first the best case shown in Tables 2-7a, 2-7b, and 2-7c, which is the long-form-sample estimate of 15 percent poor school-age children for an area with 2.5 million people. For this estimate, the relative standard error is only 1.1 percentage points, the 90 percent MOE is only ±0.3 percentage points, and the 90 percent confidence interval is quite narrow -- 14.7 to 15.3 percent.
From page 68...
... ACS estimates are not published below the solid line in column 4 (below 65,000 people) and column 6 (below 20,000 people)
From page 69...
... Census Bureau, 2005:Table C) : • 1.5 design factor for areas of 5,000 or more people, with assumed sample sizes of about 15 percent, instead of 16.7 percent, of school-age children (allowing for unit nonresponse)
From page 70...
... is plus or minus (±) the standard error of an estimate times 1.65 (see Table 2-7a notes)
From page 71...
... . The 90 percent confidence intervals in parentheses are inexact.
From page 72...
... Still, for some applications, a ballpark estimate with an even wider confidence interval may suffice. In deciding which set of ACS estimates is best suited for a particular application, users will need to make trade-offs between timeliness and sampling error.
From page 73...
... above to obtain the estimated standard error and multiply the result by 1.65. For example, the 90 percent margin of error for an ACS 1-year period estimate of 15 percent poor people in an area of 65,000 total population is 15 times 0.106 equals 1.6, times 1.65 equals ±2.6, which, in turn, gives a 90 percent confidence interval of 12.4–17.6 percent poor people.
From page 74...
... . 2-C.2.d  Documentation of Sampling Error The Census Bureau commendably is trying to impress upon users the extent of sampling error in the ACS estimates.
From page 75...
... This design produces estimates that pertain to periods of time -- averages over 12, 36, or 60 months -- instead of the traditional point-in-time estimates with which users are familiar from the long-form sample and other household surveys. Users will need to work together and with the Census Bureau to develop strategies for application of the ACS information that take account of the survey's continuous design.
From page 76...
... Moreover, the option of combining small governmental units into larger analytical units in order to improve the precision of estimates is less applicable than in the case of combining census tracts or block groups within a larger jurisdiction. Chapter 3 discusses possible strategies for data users who are interested in very small governmental units to make effective use of the ACS estimates.


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