American Community Survey
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Transcript of 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 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