[CTPP] ACS 5-year Federal Register Notice

I am not sure if others are pondering what the recent Federal Register notice on ACS 5-year data products really means but I believe that there are some “key” facts missing. Facts that would allow users’ the ability to asses the true impact of the rules. For example: Rule 7 of the Disclosure Avoidance rules states that “For the residence and workplace tables where means of transportation (mode) is crossed with one or more other variables, there must be at least three unweighted workers in sample for each transportation mode in a given place for the table to be released. Otherwise the data must be collapsed or suppressed and complementary suppression must be applied. There is no threshold on univariate tables.” http://www.census.gov/acs/www/Downloads/proposal_acs5yearproducts.pdf While this might sound very straight forward we know from the “statistical collapsing” rules that were applied to the 3-year data that only one collapsing attempt is made of the data and if the table does not pass it is tossed out (suppressed). What we do not know about the current rule is what will the collapsing hierarchy be, and will the Census continue collapsing modes into each other until the threshold is met? Both the Federal Register notice and the rules are silent on this issue. In some recent work done for FHWA by the Census Bureau we do know that at a Tract level a great deal of data will be suppressed under Rule 7. Using 5-year data from five of the ACS test counties, Multnomah, Lake, Broward, San Francisco and Bronx we do know that if all 17 modes (means of transportation) are used only 3 to 8 percent of the Tracts would have enough data to be released. However, if we cut the number of modes down to only 4 including Drove Alone, Carpooled, Transit, and other including work at home somewhere between 5 and 37 percent of the tables will be suppressed. And that is at the TRACT level! If per chance someone wants to go one step up the modal ladder and split out “bike and walk” and make work at home a separate category yielding 6 modal categories, upwards of 80 percent of the TRACT level tables can expected to be suppressed. At the Block Group the suppression will be only worse. -- Ed Christopher Resource Center Planning Team Federal Highway Administration 19900 Governors Drive Olympia Fields, Illinois 60461 708-283-3534 (V) 708-574-8131 (cell) 708-283-3501 (F)