American Community Survey

http://edthefed.com/

• 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 WorkMeans of Transportation to Work

Carpool Occupancy to WorkDeparture Time for Work

Travel Time to WorkVehicles 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 Cheese2. MOEs (Significance Tests)3. Collapsing4. Reliability/Currency5. Current Geography6. Dollar Values7. Light Rail Conundrum8. Weighting9. Urban Area Population10. Finding Stuff11. 5-year ACS

NE Illinois (2009ACS3)Gray = Less than 20K people and No data

““Where’s the Where’s the beefbeef Data?” Data?”

““It Looks Like Swiss Cheese”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 2005-2007 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

22 (SE(B))(SE(A))

BAZ

4. If Z < -1.645 or Z > 1.645Difference 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

http://www.census.gov/acs/www/guidance_for_data_users/compass_products/

A Compass for Understanding And Using ACS Data

Set of user-specific handbooks

Train-the trainer materialsE-learning ACS Tutorial

Annotated Presentations

Especially

Appendix 3

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/

The CUTR Guide has you covered

and a Spreadsheet Calculator

http://www.nctr.usf.edu/pdf/77802.pdf

There’s a Report

http://www.nctr.usf.edu/spreadsheet/77802.xls

http://www.nctr.usf.edu/abstracts/abs77802.htm

Transportation Resources

http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_588.pdf

Power Point slide presentation with a step by step example of a significance testhttp://www.edthefed.com/presentations/significance%20testing.ppt

TRB Census Subcommittee Listserve

http://trbcensus.com/maillist.html

14

Final Word on MOEs

3. Collapsing

“B” and “C” Tables

C08301. MEANS OF TRANSPORTATION TO WORK - Universe: WORKERS 16 YEARS AND OVERData Set: 2007-2009 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

http://www.census.gov/acs/www/guidance_for_data_users/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 AFFConcern over large MOEsOn 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) http://www.copafs.org/UserFiles/file/HodgesMarch2011.pptx

BG data recommended only for aggregations

Data Evolution?

http://edthefed.com/

ACS Data, Things to know

Ed ChristopherResource Center Planning TeamFederal Highway Administration 4749 Lincoln Mall Dr. Rm 600Matteson, IL 60443

708-283-3534edc@EdtheFed.com