American Community Survey

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 What is the ACS? Place of Work Means of Transportation to Work Carpool Occupancy to Work Departure Time for Work Travel Time to Work Vehicles Available  

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

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 year ACS

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

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

You must do Statistical Significance Tests To avoid invalid statements like “Based upon data from the 2000 Census (CTPP) and the ACS, the total number workers who 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 Commutes Increase for all Modes

How do you do a Significance Test? 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 Difference is Significant at 90% confidence It is simpler than it looks and there are a lot guides

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

The ACS compass handbooks A Compass for Understanding And Using ACS Data  Set of user-specific handbooks  Train-the trainer materials  E-learning ACS Tutorial  Annotated Presentations Especially Appendix 3

NY State Data Center Calculator t-to-calculate-acs-margins-of-error-and-statistical- significance-for-sums-proportions-and-ratios/

The CUTR Guide has you covered and a Spreadsheet Calculator There’s a Report

Transportation Resources linepubs/nchrp/nchrp_rpt_ 588.pdf Power Point slide presentation with a step by step example of a significance test TRB Census Subcommittee Listserve

14 Final Word on MOEs

3. Collapsing

“B” and “C” Tables

C MEANS OF TRANSPORTATION TO WORK - Universe: WORKERS 16 YEARS AND OVER Data Set: American Community Survey 3-Year Estimates Collapsed table Full table not available Sometimes neither tables exist Less collapsing with ACS5 tables

Full and collapsed table

4. Reliability/Currency

5. Current Geography ACS uses the geography for the current year of the data release Places   annually PUMAs, Tracts, Block Groups   every 10 years Counties   seldom

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

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

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

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

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

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

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 Ken Hodges, Nielsen (claritas) ACS 5-Year Data: A First Look at the First Release (4.5 MB, ppt) ACS 5-Year Data: A First Look at the First Release BG data recommended only for aggregations

Data Evolution?

ACS Data, Things to know Ed Christopher Resource Center Planning Team Federal Highway Administration 4749 Lincoln Mall Dr. Rm 600 Matteson, IL