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American Community Survey

Learn about the methodology and key features of the ACS, including sample size, response rates, and the types of data available. Explore topics such as transportation, population estimates, significance tests, collapsing tables, and more.

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American Community Survey

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  1. American Community Survey http://edthefed.com/

  2. What is the ACS? • Continuous Survey Methodology • 250,000 Households sampled per month • About 1 in 40 Households sampled per yr • Response rates are lower than long form • Same transportation questions as 2000 long form Place of Work Means of Transportation to Work Carpool Occupancy to Work Departure Time for Work Travel Time to Work Vehicles Available € B

  3. Data Comes out Annually • Annual estimates • (places over 65K pop) • ACS1 • 3-year estimates • (places over 20K pop) • ACS3 • 5-year estimates • (all places, Tracts, Block Groups) • ACS5 Period Estimates

  4. List of Issues 1. Swiss Cheese 2. MOEs (Significance Tests) 3. Collapsing 4. Reliability/Currency 5. Current Geography 6. Dollar Values 7. Light Rail Conundrum 8. Weighting 9. Urban Area Population 10. Finding Stuff 11. 5-year ACS

  5. X “Where’s the beef Data?” “It Looks Like Swiss Cheese” 1. Swiss Cheese (ACS1, ACS3) NE Illinois (2009ACS3) Gray = Less than 20K people and No data Swiss Cheese Effect

  6. 2. Margins of Error (MOEs) • All ACS data comes with a published MOEs • Size depends on series (ACS1, ACS3, ACS5 ) and Geography • MOEs estimated at 90% confidence I am 90% sure that the percent of people carpooling to from my hometown of Berwyn, IL which is around 55K people is somewhere between 10 and 15.4 percent

  7. You must do Statistical Significance Tests To avoid invalid statements like Commutes Increase for all Modes “Based upon data from the 2000 Census (CTPP) and the 2005-2007 ACS, the total number workerswho live in Flagstaff increased along with the number who took transit to work. During the same time, the number of people who worked at home increased along with those who drove alone and carpooled.”The World Gazette

  8. 1.Get the Margin of Error (MOE) from ACS 2. Calculate the Standard Error (SE) [SE = MOE / 1.645] 3. Solve for Z where A and B are the two estimates 4. If Z < -1.645 or Z > 1.645 Difference is Significant at 90% confidence How do you do a Significance Test? It is simpler than it looks and there are a lot guides

  9. Some things to keep in mind • Obtaining Standard Errors is the Key • Formulas vary depending comparisons • Sum or Difference of Estimates • Proportions and Percents • Means and Other Ratios • Working with 2000 data will be a little more involved There are resources to help

  10. A Compass for Understanding And Using ACS Data l Set of user-specific handbooks l Train-the trainer materials l E-learning ACS Tutorial l Annotated Presentations The ACS compass handbooks Especially Appendix 3 http://www.census.gov/acs/www/guidance_for_data_users/compass_products/

  11. NY State Data Center Calculator http://sdcclearinghouse.wordpress.com/2009/03/03/spreadsheet-to-calculate-acs-margins-of-error-and-statistical-significance-for-sums-proportions-and-ratios/

  12. The CUTR Guide has you covered There’s a Report http://www.nctr.usf.edu/pdf/77802.pdf and a Spreadsheet Calculator http://www.nctr.usf.edu/spreadsheet/77802.xls http://www.nctr.usf.edu/abstracts/abs77802.htm

  13. Transportation Resources http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_588.pdf TRB Census Subcommittee Listserve http://trbcensus.com/maillist.html Power Point slide presentation with a step by step example of a significance test http://www.edthefed.com/presentations/significance%20testing.ppt

  14. Final Word on MOEs

  15. 3. Collapsing

  16. “B” and “C” Tables

  17. Collapsed table Full table not available Sometimes neither tables exist Less collapsing with ACS5 tables

  18. Full and collapsed table

  19. 4. Reliability/Currency

  20. 5. Current Geography ACS uses the geography for the current year of the data release Placesrannually PUMAs, Tracts, Block Groupsrevery 10 years Countiesrseldom http://www.census.gov/acs/www/guidance_for_data_users/geography/

  21. 6. Dollar Values and Income tables ACS asks-- What was your income during the last 12 months? Single Year Estimates 12 different periods Each adjusted to single period (Jan to Dec) Multiyear Estimates Each year adjusted to current year Dollar values adjusted to current year of the data release

  22. 7. Light Rail Conundrum Impact of New “Light Rail” systems might not be showing up Source: 2000 CTPP and 2007ACS3, CTPP Data Profile 1

  23. 8. Weighting ACS is weighted to Annual Pop Estimates but not reweighted when the estimates change even though the older estimates get revised 2010 actual population 3,817,117

  24. Change in Weighting In 2009 Census changed to using sub-county totals as opposed to just county totals Detroit 2010 Population 713, 777

  25. 9. Urban Area Population Totals UA totals show up in ACS but might not reflect the actual UA population Births, Deaths, Migration done at county level Not sure how the sub-county pop estimates will affect this

  26. 10. Finding Stuff Average Travel Time? (Not in Detail Tables--see Subject Tables) Work Place Tables (ACS1 and ACS3 only (8400 to 8500 series) (To find Look “for Workplace geography”) Finding the right table (Means of Transportation to Work 8300 series after all the MOT crosstabs) Takes Patience

  27. 11. 5-year ACS Large MOEs; Less Collapsing? NO Workplace Tables; Block Group data in Download area only; • Block Group data • Not on AFF • Concern over large MOEs • On Summary File only • More difficult to use • A way to screen out novice users • BG data recommended only for aggregations Ken Hodges, Nielsen (claritas)ACS 5-Year Data: A First Look at the First Release (4.5 MB, ppt) http://www.copafs.org/UserFiles/file/HodgesMarch2011.pptx

  28. Data Evolution? http://edthefed.com/

  29. ACS Data, Things to know Ed Christopher Resource CenterPlanning Team Federal Highway Administration 4749 Lincoln Mall Dr. Rm 600 Matteson, IL 60443 708-283-3534 edc@EdtheFed.com

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