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CHAPTER 8 Survey Development and Analysis Using ACS Data This section describes survey development and analysis as common applications of Census Bureau data and shows the potentially important transportation planning uses of ACS. Section 8.1 defines the different components of survey development and analysis, describes how census data can be used for survey development, and presents some specific examples of census data used for this purpose. Section 8.2 describes some benefits and limitations of shifting from cen- sus to ACS data related to survey development and analysis. Finally, Section 8.3 provides a case study that shows how to do survey expansion using ACS data and how the results compare to survey expansion using Census data. 8.1 Survey Development and Analysis Census data are used in multiple aspects of household travel survey development efforts, including sample design, survey expansion, and survey validation. Sample design is the process of determining the sample size needed to achieve a certain level of confidence, and/or the categories that should be used in a stratified sample design. Survey expansion is the process of creating weights for survey responses and applying these weights to expand the survey to the entire population of a given area so as to adjust for sam- pling and non-sampling errors. Survey validation is the process of checking variables that were not controlled in the sample design (or expansion) for biases (e.g., checking whether income groups are well represented in a sample designed by vehicle ownership and household size.95) 8.1.1 Using Census Data for Survey Development Census data assist in survey development and analysis in several ways, including the following: Census data are used to estimate the incidence of households with certain characteristics within a geographic area, so that the cost of reaching less common groups and completing cer- tain minimum numbers of households within those groups can be assessed. Census data also help determine the number of categories needed in a stratified sample design. For example, analysts use the data to determine which auto ownership categorization makes the most sense for sample stratification and modeling. Census data are critical for providing control totals needed in survey expansion efforts. Sur- vey expansion based on variables such as population or households is often performed using 95 U.S. DOT and Bureau of Transportation Statistics, 1996, "Implications of Continuous Measurement for the Uses of Census Data in Transportation Planning." 131