AASHTO & FHWA Appeal re:

DRB “rule of three” decision

before the

Data Stewardship Executive Policy Committee

8/28/2008

Why we are here – in broad terms

1. The ACS-based Census Transportation Planning Products (CTPP) program is critical to investment decisions of hundreds of billions of dollars, as well as environmental, safety and homeland security issues

2. CTPP is a core data program of federal/state and metropolitan transportation planning and administrative agencies that is now threatened by the DRB action

• CTPP tables request in late February 2008

• DRB ruling “3 unweighted records PER CATEGORY of Means of Transportation to work” in cross-tabulations.

• DRB ruling is onerous and will suppress many tables, even when geography is large (population threshold = 20,000) and the categories for Means of Transportation are reduced

• We believe the threshold rule is unnecessary. Even when the rule is removed the CB will still maintain individual confidentiality

Why we are here – SpecificallyCTPP table request using ACS samples

(2005-2006-2007)

Means of Transportation to Work17 categories-- full list

10 categories -- Collapsed

Drove Alone

Carpool- 2

Carpool -3

Carpool – 4 or more

Bus

Streetcar, subway, elevated

Railroad, ferry

Bicycle or walked

Taxi, motorcycle, other

Worked at home

The AASHTO/FHWA position • It is our view that in this application

– Present disclosure safeguards are entirely adequate to protect confidentiality

– Present CTPP consistent with previously acceptable approaches

– The proposed DRB “rule of three” has not been supported by evidence

– All evidence points to the contrary– Imposition of the rule will effectively destroy

CTPP program and our support for ACS. (up to 80% of areas affected)

New rule for 3-year CTPP isfar more onerous than for others

ACS

(Micro data)

1%

Census 2000 LF

Tract

CTPP

2000

TAZ or BG

“NEW”

CTPP with ACS

Population 100,000 4,000 1,200 20,000

Estimated unwgtedsample (persons)

1,000 500-600 150-200 800

Protections

1. ACS Survey Design and Collection

2. Survey Processing and Post-

processing (including tabulations)

1. ACS Survey Design and Collection

• Small sample (about 4% after 3 years)

– Address Based – not person based sample

• 36 months of data accumulation

– Changes over time, especially residential moves, workplace changes, and related changes, esp. to journey-to-work

– Period Estimate not point in time

• Question wording “usually get to work last week”

2. Survey Processing and Post-processing (including tabulation)

• Complex weighting scheme

• Data Swapping

• Imputation

• Tables, not microdata

• Tabulation limited to large geog (20,000+ pop)

• Variables collapsed and grouped

• Data averaging and adjusting (moving the income values to last year e.g. 2007)

AASHTO commissioned data-driven disclosure risk analysis

• Research conducted by Westat• Emulated Snooping using Intruder Scenario• Important findings:

– Confirmed Risk vs Data Utility imbalance– Pseudo-Micro data addressed — “file” risk is extremely

low – “Individual” Risk-level is low- Similar to ACS annual

PUMS– Recommendation to drop DRB restrictions on 3-year

CTPP– Mode to Work, critical to users and not a critical

disclosure risk variable

Worst case

• 3 in 100 chance of identifying an individual record

• Data snooper would have to: – Create a pseudo-micro record using cross-

tabulated table cell labels as variables and match to the ACS PUMS to gain additional detailed variables

– Find a high quality external file (e.g., publicly available person-level registry or a confidential data set), that have personal identifiers (name, address, etc)

– Find a unique record in external file that matches CTPP/ACS micro record

Ultimate Disclosure test

Not the identification of a unique record at issue

“It is against the law to disclose or publish any private information that identifies an individual or business:

No namesNo addressesNo Social Security NumbersNo telephone numbers”

www.census.gov/privacy/files/data_protection/002777.html

We Face a Policy Challenge

• We have invested a fortune in this program

• We were sold the new ACS program based on its greater utility in our work

• We have been among the strongest supporters of the program

• The Bureau has not been helpful in addressing the challenges of ACS

• The Bureau has used the transportation support as a major argument for the benefits of the ACS products

Conclusion

• The Data Stewardship Executive Policy Committee should find that existing safeguards are effective and adequate to the task of protecting confidentiality in this application, and

• The Data Stewardship Executive Policy Committee should not permit “the rule of three” disclosure rule to be instituted at this late stage in this application

BUT,

IF WE CANNOT GET WHAT WE NEED AND EXPECTED FROM THE ACS

WE WILL BE FORCED TO WALK AWAY FROM THE PLANNED CTPP PROGRAM WITH THE CENSUS BUREAU

WHICH WILL SHARPLY DIMINISH THE SENSE OF THE VALUE OF THE ENTIRE ACS PROGRAM!

Thank you !

Jack Basso, AASHTO Gloria Shepherd, FHWA Alan Pisarski, ConsultantRon McCready, AASHTO Elaine Murakami, FHWA Ed Christopher, FHWA Mark Freedman, Westat Tom Krenzke, Westat