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ACS products can be accessed easily through the Census Bureau American FactFinder site (http://factfinder.census.gov/home/saff/main.html). From this main page, as shown in Figure 3.1, data users can quickly obtain census facts about specific geographic areas, and can select the Census Bureau data product that they are trying to access. The âlearn moreâ tab provides users with an overview of ACS and its uses, and includes a link to the Census Bureauâs American Community Survey site that includes detailed information about all aspects of ACS. The âget dataâ tab brings users to the ACS datasets web page, as shown in Figure 3.2, where users can select a strategy for obtaining the data that they need. Included on the ACS datasets page are links to the Census Bureauâs âDraft Quick Guides to the American Community Survey.â The 2005 guide is located at www.census.gov/acs/www/ Products/users_guide/index.htm. The quick guides provide the most up-to-date specific procedures for obtaining ACS data. When new data become available, new data products are developed, and the American FactFinder website is modified and improved over time, users should obtain the most current quick guide. The Census Bureau also is developing a CD-ROM- based user guide with simple case studies and exercises for data users to become more familiar with ACS data products. Although the Census Bureau websiteâs specific format and the specific instructions in the Census Bureau quick guides will probably change slightly over time, the process for obtaining data is likely to remain close to what it is now, which is as follows: 1. Select the dataset year. 2. Select the data product. 3. Provide the geography to be analyzed using drop-down lists of available Census geographic areas. (The Census Bureau provides an on-screen mapping option to allow users to ensure that the selected geography is correct.) 4. Provide additional table specifications as required by the particular data product. 5. Obtain results. (The requested data product is provided on screen, and users can download the results in a variety of file formats, including comma delimited, tab delimited, rich text format, or Microsoft Excel.) 3.1 ACS Data Products The basic ACS data products include â¢ Base Tables (or Detailed Tables), â¢ Data Profiles, â¢ Multiyear Profiles, 22 C H A P T E R 3 Obtaining ACS Data
â¢ Ranking Tables, â¢ Thematic Maps, â¢ Subject Tables, â¢ Selected Population Profiles, and â¢ Public Use Microdata Sample (PUMS) Database. These products are summarized in the remainder of this section. With the exception of the PUMS database, examples of these products are included in Appendices B through H at the end of this guidebook. The data products can be found fairly easily on the American FactFinder site but, if necessary, users can refer to the Census Bureau quick guide to determine how to locate these products on the website. 3.1.1 Base Tables Base Tables, or Detailed Tables, are straightforward descriptive tabulations of basic ACS vari- ables and concepts. These tables are likely to be the most commonly used for focused, custom analyses of ACS data. Base Tables are used when one needs to know a specific piece of informa- tion about a geography of interest and, as their name implies, the estimates provided in these tables are the basis of most of the other Census ACS products. Figure B.1 in Appendix B provides an example of a Base Table (or Detailed Table). Using drop-down lists, the American FactFinder data user can select from the available geographic Obtaining ACS Data 23 Access to ACS data and documentation Figure 3.1. American FactFinder website main page.
areas and detailed tables to have the base table appear on the screen. In addition, these tables may be downloaded in a variety of useful file formats, including â¢ Rich text format (.rtf), â¢ Comma delimited (.csv), â¢ Tab delimited (.lst), â¢ Microsoft Excel (.xls), and â¢ Comma delimited database format (.txt). In addition to obtaining single Base Tables for specific census geographic areas, experienced data users can obtain up to 50 Base Tables at once for census areas for which the data are avail- able at the American FactFinder Download Center (located by following the links to http:// factfinder.census.gov/servlet/DownloadDatasetServlet?_lang=en). These downloaded data come in a zipped, comma delimited file format. The Download Center offers similar capabilities for all recent Census Bureau datasets. Table B.1 in Appendix B lists the many detailed tables that the Census Bureau has made available for the 2004 ACS. Note that several of these tables are commonly used by trans- portation planners, including especially those tables that are numbered with B08 (followed by three other characters). Some of these Base Tables, such as the workplace-based tables, had 24 A Guidebook for Using American Community Survey Data for Transportation Planning Step 1: Select ACS Data Set Step 2: Select Data Product Figure 3.2. American FactFinder ACS datasets page.
only been available as part of the Census Transportation Planning Package (CTPP) for the decennial census. Their inclusion as ACS Base Tables means that transportation planners will be able to obtain these tables consistently within nine months of the end of the data collection period, rather than having to wait for any special tabulation. ACS Base Tables will be available at all census geographic levels, from the national level down to the smallest reportable geographic levels (block group level and above). Figure 3.3 summa- rizes the census geographic levels. A discussion of census geography can be found on the Census Bureau website. For the 2004 ACS, only state, large county, and large places have single-year detailed tables available, but with full implementation of ACS beginning in 2005 and 2006, over time the tables will be expanded to all census geographic areas. Tables for smaller geographic areas will be Obtaining ACS Data 25 American Indian Area/Alaska Native Area/Hawaiian Home Land ANRC: AIANHH: Alaska Native Regional Corporation SLD: State Legislative District (upper & lower chambers) TAZ: Traffic Analysis Zone UGA: Oregon Urban Growth Area ZCTA: ZIP Code Tabulation Area NATION REGIONS Counties Voting Districts AIANHHs UGAs SLDs ANRCs Places TAZs Census Tracts Subbarrios Block Groups County Subdivisions School Districts Congressional Districts ZCTAs DIVISIONS STATES Blocks Urban Areas Figure 3.3. Hierarchy of census geographic entities.
produced for multiyear periods. Larger geographic areas will have both single-year tables and multiyear average tables. Tables B.2 and B.3 in Appendix B provide additional details on transportation-related Base Tables. Table B.2 shows the residence-based tables, and Table B.3 shows the workplace-based tables. These summaries include the population universes used in each of the tables, the num- ber of categories of each variable in the table (shown in parentheses in the table titles), and the total number of table cells. So, for ACS Base Table B08006, the Census Bureau provides estimates for three gender categories (male, female, and total) and 21 categories for means of transporta- tion (19 mode categories, a worked-at-home category, and total), for a total of 63 table cells. The table universe for that table is workers 16 years and over in the specified geographic area. Even though a particular tabulation variable is the same in two tables, the number of tabula- tion categories may vary. For instance, in Base Table B08006, Sex of Workers by Means of Trans- portation, there are 21 categories for means of transportation; in Base Table B08101, Means of Transportation to Work by Age, and in most other tables with this variable, there are seven categories for means of transportation. However, in Base Table B08136, Aggregate Travel Time to Work (in Minutes) of Workers by Means of Transportation, there are 12 categories for means of transportation, and in Base Table B08132, Means of Transportation to Work by Time Leaving Home to Go to Work, there are 6 categories for means of transportation. The tabulation categories were established by the Census Bureau in consultation with transportation data users. Table B.4 lists the variable categories used for ACS Journey to Work transportation-related variables. 3.1.2 Data Profiles Data Profiles provide users with standardized summaries of the population and housing characteristics for user-selected geographic areas. There are four types of Data Profiles â¢ General demographic characteristics, â¢ Selected social characteristics, â¢ Selected economic characteristics, and â¢ Selected housing characteristics. Examples of each of the four available Data Profiles are shown in Appendix C. In addition, the Census Bureau is beginning to offer narrative profiles that will provide narrative descriptions of key data for the population of interest. Data Profiles will be available at census geographic levels as detailed as the place and county subdivision level once the ACS small area data are reportable. For the convenience of users, and to emphasize the ACSâs use of sampling, the profiles include estimates, as well as their upper and lower bounds assuming a 90 percent confidence interval. 3.1.3 Multiyear Profiles A key advantage of the ACS is its continuous data collection that allows users to track changes, trends, and patterns from year to year. The Multiyear Profiles provide users with tables con- taining the information from the Data Profiles, but across several years. There are the same four types of Multiyear Profiles as the first four Data Profiles (demographic, social, economic, and housing). Examples of the Multiyear Profiles are shown in Figures D.1 to D.4 in Appendix D. The Multiyear Profiles provide users with an indication of whether past year estimates are significantly different from the most current yearâs estimates from a statistical viewpoint (90 percent confidence level). 26 A Guidebook for Using American Community Survey Data for Transportation Planning
3.1.4 Ranking Tables Ranking Tables allow users to compare geographic areas according to many different charac- teristics. For the 2004 ACS, there are 81 Ranking Tables. Table E.1 in Appendix E lists these tables. Five of the Ranking Tables are within the Census Bureauâs transportation subject area: â¢ Mean travel time to work; â¢ Percent of workers who traveled to work by car, truck, or van alone; â¢ Percent of workers who traveled to work by carpool; â¢ Percent of workers who traveled to work by public transportation; and â¢ Percent of workers who worked outside county of residence. Figure E.1 shows an example of a basic Ranking Table. Users also may produce ranking tables that identify statistically significant differences between one of the selected geographic areas and the other ranked areas. The tables that highlight statis- tical differences are interactive (users choose one of the rows to be compared to the others), so unlike the standard ranking tables, these tables cannot be downloaded. Figure E.2 shows a screenshot example of a Ranking Table with statistical significance testing. In addition to the tables, users also can view the rankings in a chart format, such as that shown in Figure E.3. These charts graphically depict the upper and lower bounds of the estimates (90 percent confidence interval), and therefore show the level of uncertainty in the estimates. These confidence interval charts can only be viewed and printed (but not downloaded). For 2004, Ranking Tables are available at the state, county, and place level with populations of 65,000 or more. In future releases, Ranking Tables will be available for all states, counties, and places. 3.1.5 Thematic Maps Thematic Maps show the geographic patterns for several ACS data elements (those available in the Ranking Tables) at the state level. Like the Ranking Table charts, Thematic Maps can be viewed and printed, but these files are not downloadable. Appendix F shows an example of a Thematic Map. It is possible that as more data are available for smaller areas in the future, the Census Bureau will expand the geographic areas available in Thematic Maps. 3.1.6 Subject Tables The ACS Subject Tables are a group of tables that will allow users to analyze popular topic areas and themes for individual geographic areas. With the Subject Tables, the Census Bureau has sought to combine the information in related Base Tables into single tables. Therefore, Subject Tables are broader than Base Tables, but more focused than Data Profiles. Table G.1 in Appen- dix G shows the 2004 ACS Subject Tables. It is intended that more Subject Tables will become available over time, based on user demand and Census Bureau determination of the value. Examples of currently available Subject Tables related to commuting are shown in Figures G.1 and G.2. Figure G.1 shows an example of the Place of Residence Commuting Characteris- tics by Sex Subject Table. Figure G.2 shows an example of the Means of Transportation to Work by Selected Characteristics Subject Table. Census Bureau Journey-to-Work staff have proposed a third commuting-related Subject Table, a place-of-work-based version of the Commuting Characteristics by Sex Subject Table, but this has not yet been implemented. Subject Tables will be available for all census geographic levels as the multiyear small area data become available. Obtaining ACS Data 27
3.1.7 Selected Population Profiles Selected Population Profiles will provide detailed information on selected population groups, such as people in poverty, teenagers, the elderly, workers, children, grandchildren, and immi- grants. Selected Population Profiles currently are only available on an example basis for race and ethnicity groups and for ancestry groups, but the Census Bureau has plans for making many more available over time. Appendix H shows an example of a currently available Selected Pop- ulation Profile. A potential future Selected Population Profile for Workers will include several important transportation-related tabulations. 3.1.8 Public Use Microdata Sample (PUMS) Files As for the decennial census, the Census Bureau is making a sample of actual responses to the ACS available to users so that users can create their own cross-tabulations. The Census Bureau currently releases ACS PUMS data for the statewide level. In the future, the data will be released at the state and Public Use Microdata Area (PUMA) level. The ACS PUMS is disaggregate data available at the housing unit and person levels. The Cen- sus Bureau selects a sample of housing units that filled out the questionnaires, and publishes the full range of responses from those households while protecting the confidentiality of the data. As a result, the residential geographic detail that is available from the PUMS is limited to the state level (PUMA level in the future). The workplace locations in ACS PUMS data are limited to the county level, because a substantial proportion of work locations would need to be allocated for more detailed geographic specificity. The data consist of two microdata files that can be linked to each other: one containing hous- ing unit records and the other containing person records. Since weighting factors are provided with the individual records, users can produce any desired cross-classification of variables of inter- est. In addition, the data can be used to better understanding the relationships among variables (e.g., the characteristics of households with three or more vehicles, vehicle availability discrete choice models, etc.) through regression and modeling applications. The Census Bureau will provide PUMS data as single-year products. Data users will need to aggre- gate multiple-year ACS data to create larger samples. Because they are produced annually, ACS PUMS datasets are substantially smaller than the PUMS datasets developed for the decennial census. Table 3.1 compares the number of housing units and persons in the year 2000 decennial census PUMS dataset with the number of housing units and persons in the year 2004 ACS PUMS dataset. 3.1.9 Access to Census Data Records In addition to these current and planned products, thus far for the test sites, the Census Bureau has provided ACS test site data to allow users to evaluate the data and to make comparisons with Census 2000. However, the evaluation data are for the test sites only and will generally not be available for future years. Access to actual ACS data is restricted under the Center for Economic Studies (CES) and Regional Data Center (RDC) program to Census Bureau staff and to academic researchers that demonstrate the likelihood that their analyses of these data will benefit the Census Bureauâs data collection programs, and that agree to stringent data confidentiality requirements. It is not likely that public agency transportation planners will be able to participate in this program for their applications as they tend not to be purely oriented to research. Deb Niemeier of the University of California-Davis has documented the protracted process of obtaining the necessary approvals for using RDC Services for her analysis of ACS workplace 28 A Guidebook for Using American Community Survey Data for Transportation Planning
Census 2000 ACS 2004 State Postal Abbreviation U.S. AL AK AZ AR CA CO CT DE DC FL GA HI ID IL IN IA KS KY LA ME MD MA MI MN MS MO MT NE NV NH NJ NM NY NC ND OH OK FIPS State Code 00 01 02 04 05 06 08 09 10 11 12 13 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 PUMS Housing Units 6,098,438 103,912 14,013 114,948 62,348 651,698 9,559 74,709 18,386 15,526 384,600 175,784 24,806 27,968 260,396 135,532 66,846 60,663 93,295 99,162 34,342 113,969 142,183 224,214 110,095 62,868 130,222 21,871 38,679 43,056 29,132 175,259 40,845 413,005 188,898 15,669 254,118 81,350 PUMS Population 14,081,466 222,587 31,924 259,694 133,994 1,690,642 215,520 170,658 38,906 28,605 796,421 406,582 60,948 64,389 619,232 304,060 146,399 133,658 201,784 222,482 64,133 264,242 318,565 496,765 249,237 142,459 279,675 45,887 86,083 100,429 61,684 420,692 91,783 953,076 399,813 32,530 569,795 173,843 PUMS Housing Units 514,830 7,162 3,981 8,468 4,100 45,095 7,370 5,543 4,631 3,707 28,221 12,490 4,304 4,143 19,077 10,604 8,950 7,112 10,672 8,925 4,342 9,675 10,505 17,219 8,886 8,715 9,524 4,465 5,643 4,305 4,518 12,824 4,153 27,766 13,231 4,489 19,775 5,531 PUMS Population 1,194,354 15,657 9,235 19,479 9,124 114,921 17,100 13,346 10,170 6,814 60,907 29,002 11,155 10,061 45,612 25,046 20,036 16,144 24,122 20,619 8,585 23,067 24,593 40,159 20,998 19,861 21,820 9,545 12,890 9,770 10,237 32,088 8,824 65,371 29,338 9,603 45,493 12,310 OR 41 76,516 171,666 5,939 13,610 PA 42 284,158 618,202 21,389 48,462 RI 44 23,935 52,586 4,571 10,568 SC 45 94,441 199,293 6,714 14,774 SD 46 17,586 38,013 6,251 14,022 TN 47 129,378 282,722 9,685 22,019 TX 48 435,954 1,040,527 27,186 66,385 UT 49 40,457 112,363 4,273 12,194 VT 50 15,761 30,816 4,562 9,527 VA 51 156,800 351,485 11,900 28,024 WA 53 129,378 296,440 10,354 24,146 WV 54 44,393 90,156 7,512 15,147 WI 55 123,858 272,879 10,228 23,159 WY 56 11,897 25,142 4,145 9,215 Table 3.1. Comparison of data records in 2000 decennial census PUMS and 2004 ACS PUMS.
geocoding.12 This cautionary tale underscores the poor likelihood that actual ACS data would be made available for transportation planning uses. 3.1.10 Census Transportation Planning Package (CTPP) For the last several decennial censuses, transportation planners have relied on the CTPP, a series of specialized tabulations produced by the Census Bureau and sponsored by AASHTO, that provided transportation-related estimates, including journey-to-work flow tabulations. 3.2 Additional Information Sources for Obtaining ACS Data The Census Bureau provides guidance for obtaining ACS data on their ACS website and on the American FactFinder website. The documentation is very accessible. From the ACS main guidance, webpage users can find several useful links and documents, including the following: â¢ The ACS in American FactFinder Quick Guide (discussed previously); â¢ Other guide documents, including ACS at a Glance and ACS Data Products Overview; â¢ New data product announcements; â¢ Table specifications (shells) for available and proposed new tables; and â¢ Documentation on the latest yearâs data release, such as the specific geographic coverage and new tables. The information on this web page will be continuously updated, so it is likely to be frequently visited by both new and experienced users. 30 A Guidebook for Using American Community Survey Data for Transportation Planning 12 See http://www.fhwa.dot.gov/planning/census/sfacs.pdf (accessed June 2007).