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CHAPTER 5 Policy Planning and Other Descriptive Analyses Using ACS Data Perhaps the most common and straightforward uses of census Long Form data by transporta- tion planners and other data users are descriptive analyses where the census data are summa- rized in useful ways to illuminate various characteristics of different populations of interest. This section describes how basic transportation planning descriptive analyses and data sum- maries will be affected by the migration to ACS from the decennial Long Form. Section 5.1 broadly defines the different types of descriptive analyses and how these summaries are used. This section also provides some examples of uses of census data for developing descriptive analyses. A more detailed list of specific examples of uses of census data for this purpose is provided at the end of the section. Section 5.2 describes the benefits and limitations of shifting from the Long Form to ACS data related to the development of descriptive analyses. Finally, Section 5.3 provides case study examples showing how one could develop different types of descriptive analyses using ACS data. 5.1 Descriptive Analyses Descriptive analyses are reports, summarys, charts, and/or maps that summarize the character- istics of a given population in a given year or the change in those characteristics over time. When planners are asked to provide estimates regarding the characteristics of their regional population, or of specific subpopulations, some common data sources are the Decennial Census Summary File 3, the CTPP, and PUMS files which are all derived from the census Long Form data. Agencies and city planners use descriptive analyses for different purposes such as: · Understanding the demographic, social, economic, and housing characteristics of people in their region; · Evaluating the change in certain indicators of interest over time; and · Guiding policy planning analyses (such as vehicle occupancy studies, employment concentra- tion studies, corridor studies, etc.), environmental justice analyses, and other miscellaneous applications. 5.1.1 Examples of Descriptive Analyses As discussed above, the Census Bureau provides data users with several packaged products for performing descriptive analyses in addition to the actual datasets from which users can perform their own descriptive analyses. The Census Bureau's American FactFinder website provides quick and easy on-line access to data tables and thematic maps. On their website, the Census Bureau provides ready-made demographic profile tables at the state, county, and place level of geography (places with more 73
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74 A Guidebook for Using American Community Survey Data for Transportation Planning than 25,000 population), comparison and ranking tables, Census briefs, and Census special reports. These descriptive analysis products provide most data users, particularly infrequent users, with the summaries that they require. In addition, the decennial census datasets are made avail- able to users who frequently need to perform more detailed, ad hoc descriptive analyses. 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. The special tabulation and mapping software that is available with the CTPP data allow users to perform descriptive analyses on issues of particular interest to the transportation community. Figures 5.1, 5.2, and 5.3 show examples of how some researchers have presented descriptive analyses of Census Bureau data.43 Figure 5.1 provides a thematic map showing mean travel time ranges by county. Figure 5.2 provides a bar chart showing mean travel time by county. Figure 5.3 provides a pie chart showing the distribution of workers by mode of transportation to work. A list of some more specific examples of using Census data to do descriptive analyses also is provided at the end of this section. 5.1.2 ACS for Descriptive Analyses As for the products based on the census 2000 Long Form, the ACS data releases described in Section 3 of this guidebook provide most data users with very efficient means of obtaining the Figure 5.1. Mean travel time to work distribution by county. 43 These figures are obtained from the Missouri Department of Transportation Socio-Economic Indicator Resource web page at http://oseda.missouri.edu/modot/planning/northcentral_transportation.shtml.
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Policy Planning and Other Descriptive Analyses Using ACS Data 75 Sullivan 21.2 Schuyter 25 Saline 17.1 Randolph 21.1 Putnam 26.7 Mercer 24.8 Macon Livingston 21.3 Linn 18.2 Howard 20.8 Grundy 25.3 Chariton 19.6 Carroll 23.4 Adair 26.5 14.7 0 5 10 15 20 25 30 Mean Travel Time to Work (in Minutes) Source: USDC, Bureau of Census, Census of Housing and Population, Summary File 3 (2000) Produced by: The Office of Social and Economic Data Analysis, UOE (TDranginis, August 2002) Figure 5.2. Mean travel time to work by county, 2000. descriptive data that they need. Users also will have access to the available ACS data and PUMS files on a frequent and regular basis. Although special transportation-related tables based on ACS, similar to CTPP, have not been defined as of yet, the Census Bureau has included some of the most commonly used transporta- tion data items in the base data release, and the Census Bureau appears to still be interested in providing special tabulations to its many various user groups. As part of the research effort that included this guidebook, recommendations for a future CTPP product also were developed. Therefore, the general ability of users to perform descriptive analyses of the types most com- monly performed will remain as the Census Bureau completes the migration to ACS. Worked at Home 5% Other Means Drove Alone 1% 76% Walked 4% Carpooled Public 14% Transportation 0% Source: USDC, Bureau of Census, Census of Housing and Population, Summary File 3 (2000) Produced by: The Office of Social and Economic Data Analysis, UOE (TDranginis, August 2002) Figure 5.3. Distribution of workers by mode of transportation to work.