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CHAPTER 3 Obtaining ACS Data 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 "learn more" tab provides users with an overview of ACS and its uses, and includes a link to the Census Bureau's American Community Survey site that includes detailed information about all aspects of ACS. The "get data" 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 Bureau's "Draft Quick Guides to the American Community Survey." 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 website's 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 Base Tables (or Detailed Tables), Data Profiles, Multiyear Profiles, 22

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Obtaining ACS Data 23 Access to ACS data and documentation Figure 3.1. American FactFinder website main page. Ranking Tables, Thematic Maps, Subject Tables, Selected Population Profiles, and 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

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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. 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 Rich text format (.rtf), Comma delimited (.csv), Tab delimited (.lst), Microsoft Excel (.xls), and 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

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Obtaining ACS Data 25 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 NATION REGIONS AIANHHs DIVISIONS ZCTAs STATES Urban Congressional Areas Districts UGAs School Counties SLDs Districts ANRCs Voting Districts Places County TAZs Subdivisions Census Tracts Subbarrios Block Groups AIANHH: American Indian Area/Alaska Native Area/Hawaiian Home Land Blocks ANRC: 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 Figure 3.3. Hierarchy of census geographic entities.

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26 A Guidebook for Using American Community Survey Data for Transportation Planning 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 General demographic characteristics, Selected social characteristics, Selected economic characteristics, and 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 ACS's 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 year's estimates from a statistical viewpoint (90 percent confidence level).

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Obtaining ACS Data 27 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 Bureau's transportation subject area: Mean travel time to work; Percent of workers who traveled to work by car, truck, or van alone; Percent of workers who traveled to work by carpool; Percent of workers who traveled to work by public transportation; and 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.

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28 A Guidebook for Using American Community Survey Data for Transportation Planning 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 Bureau's 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

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Table 3.1. Comparison of data records in 2000 decennial census PUMS and 2004 ACS PUMS. Census 2000 ACS 2004 State Postal FIPS PUMS PUMS PUMS PUMS Abbreviation State Code Housing Units Population Housing Units Population U.S. 00 6,098,438 14,081,466 514,830 1,194,354 AL 01 103,912 222,587 7,162 15,657 AK 02 14,013 31,924 3,981 9,235 AZ 04 114,948 259,694 8,468 19,479 AR 05 62,348 133,994 4,100 9,124 CA 06 651,698 1,690,642 45,095 114,921 CO 08 9,559 215,520 7,370 17,100 CT 09 74,709 170,658 5,543 13,346 DE 10 18,386 38,906 4,631 10,170 DC 11 15,526 28,605 3,707 6,814 FL 12 384,600 796,421 28,221 60,907 GA 13 175,784 406,582 12,490 29,002 HI 15 24,806 60,948 4,304 11,155 ID 16 27,968 64,389 4,143 10,061 IL 17 260,396 619,232 19,077 45,612 IN 18 135,532 304,060 10,604 25,046 IA 19 66,846 146,399 8,950 20,036 KS 20 60,663 133,658 7,112 16,144 KY 21 93,295 201,784 10,672 24,122 LA 22 99,162 222,482 8,925 20,619 ME 23 34,342 64,133 4,342 8,585 MD 24 113,969 264,242 9,675 23,067 MA 25 142,183 318,565 10,505 24,593 MI 26 224,214 496,765 17,219 40,159 MN 27 110,095 249,237 8,886 20,998 MS 28 62,868 142,459 8,715 19,861 MO 29 130,222 279,675 9,524 21,820 MT 30 21,871 45,887 4,465 9,545 NE 31 38,679 86,083 5,643 12,890 NV 32 43,056 100,429 4,305 9,770 NH 33 29,132 61,684 4,518 10,237 NJ 34 175,259 420,692 12,824 32,088 NM 35 40,845 91,783 4,153 8,824 NY 36 413,005 953,076 27,766 65,371 NC 37 188,898 399,813 13,231 29,338 ND 38 15,669 32,530 4,489 9,603 OH 39 254,118 569,795 19,775 45,493 OK 40 81,350 173,843 5,531 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