Give a Second Thought to the Secondary City: New Applications of the USPS City State File
Derick Brown
RTI International
Joe McMichael
RTI International
As address-based sampling (ABS) has become the most prevalent method for implementing mail and in-person surveys of the U.S. household population, techniques to improve the implementation of such surveys are still being uncovered. The purpose of this paper is to discuss an underutilized data file and methods we have developed with it to improve the quality of ABS frames and field work. The United States Postal Service leases a data product called the City State file. Among other data elements, this file contains a crosswalk of every ZIP code in the U.S. to the city names associated with each ZIP code. There is a "preferred last line" city for each ZIP code, and then additionally a series of "secondary cities" associated with each ZIP code. Some ZIP codes have no secondary cities, others have upwards of thirty. Our research suggests that the secondary city is an often-underutilized tool that can improve the implementation of ABS methods in the following ways. (1) Improve geocoding accuracy and precision of addresses on an ABS frame, (2) match field enumerated addresses to a known ABS frame, and (3) assist with location of addresses on the ground during field work.