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Data issues with the American Community Survey

Data issues with the American Community Survey. Elaine Murakami, FHWA Elaine.murakami@fhwa.dot.gov. AMPO Travel Modeling Work Group, September 8, 2005. First, the good news…. CB has added several transportation-related tables to their planned set of ACS tabulations. See handouts.

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Data issues with the American Community Survey

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  1. Data issues with the American Community Survey Elaine Murakami, FHWA Elaine.murakami@fhwa.dot.gov AMPO Travel Modeling Work Group, September 8, 2005

  2. First, the good news… • CB has added several transportation-related tables to their planned set of ACS tabulations. See handouts. • This includes • Residence tabulations of households such as: household size * # of vehicles • A FEW tables by Place of Work

  3. More positive things about ACS • The ACS will provide reliable data for large geographic units on an annual basis. • The flip side is that the data for small areas will be compromised, with much larger standard errors, and the risk of the inability to tabulate small area (TAZ) home-to-work flows.

  4. Questions for today’s discussion • Do you want home-to-work flow (Part 3) from ACS if TAZs are larger, or TAZ-groups need to be used? • Should AASHTO to sponsor a pooled fund for a CTPP from ACS? AASHTO SCOP has established Census Working Group, chaired by Jonette Kreideweis at MN DOT. Jonette.Kreideweis@dot.state.mn.us

  5. Key issues for Transportation • Sample size / geographic level of reporting / data quality / error • Thresholds for FLOW tabulation • CB Disclosure Review Board

  6. Sample Size and Unweighted Responses • The number of addresses in the ACS sample is about 12.5 percent (over 60 months), compared to 16.6 percent in the decennial Long Form. • The number of unweighted records in the ACS sample is 40 to 60 percent that of the decennial Long Form.

  7. Implications of smaller number of completed surveys • Kiss TAZ-to-TAZ data GOODBYE, or define larger TAZs for Census tabulation. • Need a geographic unit maybe a “Tract Group” or a TAZ-Group that is as large as 2 or 3 tracts together, especially for home-to-work flow data.

  8. Thresholds required for CTPP2000 for flow tabulation • Thresholds are based on unweighted records. • The smaller number of completed records in ACS results in a loss of O/D pairs meeting the threshold.

  9. Impact of Thresholds Comparing Decennial LF to ACS Part 3Broward County, FL Tract-to-Tract 22% of O/D pairs 30% of workers 8% of O/D Pairs

  10. Does 60 months of accumulation result in reduced risk of disclosure? We think “yes” • People move residence • People move workplace location • People change means of transportation to work. • People change departure time. • People change # of vehicles in hhld.

  11. What rules will the DRB impose? Will the DRB impose thresholds for flow tabulation? • We hope not! • If the threshold is 3 for key tables, as in 2000, will transportation planners find it useful or not?

  12. What do we want from the CB? • Alternatives to rounding and thresholds for disclosure avoidance. • Improved allocation procedures. Want to continue working with CB on allocation and imputation of means of transportation, # of vehicles, and place of work geocoding.

  13. How should we augment ACS data? • Explore alternatives for Home-to-Work Flow matrices, including LEHD • Consider workplace surveys • NPTS for 2007, for trip length distribution curves for various trip purposes/activities • New technology approaches for O/D matrices (GPS, RFID, etc)

  14. Questions for today’s discussion • Do you want home-to-work flow (Part 3) from ACS ? • Should AASHTO sponsor a pooled fund for a CTPP from ACS?

  15. AASHTO pooled fund Potential concepts: Geography • New TAZ definition in 2008, input to TIGER • New geographic unit: “TAZ-Groups” for Flow tabulation?

  16. AASHTO pooled fund Potential concepts: Table content • Special Tables for large geographic units starting in 2007? 2008? Or, are the standard tabulations by CB sufficient? • Tables for areas with complex transit, where “bus” and “other transit” is insufficient. • Tables with Income using TAZ-Group, and eliminating Income as a variable for TAZ flows.

  17. AASHTO pooled fund Potential concepts: Add a research component • Alternatives to thresholds for disclosure avoidance. • Alternatives to “income” as a tabulation variable. • Improving business locations (esp. multisite businesses) used in the LEHD program. • Methods to combine ACS with LEHD (administrative records).

  18. Last remarks • TRB Conference on Census and ACS should have final report available on web by end of the year. • NCHRP 08-48 ACS Guidebook should be complete by end of the year • Please complete the AASHTO CTPP User Survey at http://surveys.transportation.org/ctpp.htm

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