Caleb Miller Population Division United States Census Bureau

1. Publically Available Migration Data Based on Administrative Records: A Discussion of Current and Future Data and Methods Caleb Miller Population Division United States Census Bureau For presentation at The 2010 Annual Meeting of the Association of Public Data Users Washington, DC September 20, 2010 This paper is released to inform interested parties of research and to encourage discussion. Any views expressed on methodological issues are those of the author and not necessarily those of the U.S. Census Bureau.

2. Outline • Overview • Data/Methods • Current Products • Analysis • Future Plans • Summary/Conclusion

3. Overview • This session, “Tracking Population Migration,” sponsored by the Association of Public Data Users, focuses on population migration. • The Internal Revenue Service (IRS) and the U.S. Census Bureau work together to produce a publically available migration product. • Distributed by the IRS on the IRS website • http://www.irs.gov/taxstats/article/0,,id=212695,00.html • Free data post 2005 • Pay for data pre 2005 • This presentation will discuss the inter-agency relationship, data and methods used to build this data product as well as future plans.

4. Overview • The U.S. Census Bureau is allowed access to annual tax return data to support our mission of developing federally mandated, annual population estimates for the nation’s states and counties. • We use these data to produce domestic migration rates for use within the cohort component model of population estimation. • The data displayed in this presentation differ from the Population Division’s official domestic migration statistics. • Tax data allow the U.S. Census Bureau to measure the geography and frequency of domestic migration.

5. Data/Methods • The IRS produces an annual data extract for the Census Bureau that contains administrative data collected for every 1040 tax form processed by the IRS. The data contain: • Tax Filing Units • The filer and spouse of filer, plus all exemptions represented on the forms. • Nine Digit Zipcode • ZIP+4

6. Data/Methods • The total number of exemptions per tax return is based on the total number of exemptions reported by the filer. • A ‘Return-based’ migration totals method. • Different from a ‘Person-based’ method described later. • The geography of exemptions are based on the address listed on the tax return.

7. Data/Methods • The nine digit zipcode associated with a tax return, used to represent where the tax filer and his/her exemptions live, is geocoded using a ZIP+4-to-county correspondence file. • The file contains all the ZIP+4s for a given state and/or county and/or statistical equivalent. • Geocoding the tax data with the correspondence file allows one to determine the geography of migration.

8. Data/Methods • Consecutive year tax data, X to X+1, is matched. • Residence in Year X = Migration Origin • Residence in Year X+1 = Migration Destination • If Residence in Year X = Residence in Year X+1 then no migration has taken place (non-migrants). • If Residence in Year X ≠ Residence in Year X+1 then migration has occurred (migrants). • The total number of in-migrants, out-migrants, and non-migrants for a given level of geography (U.S. , state, and county) are determined by the summation of individual tax exemptions at that level of geography.

9. Current Products • Once the tax data have been received, geocoded, matched, aggregated and suppressed by the U.S. Census Bureau, a final dataset is prepared for the Statistics of Income Division of IRS (SOI) . • Data suppression is introduced to protect the confidentiality of individual taxpayer data. • The data contain the total number of returns and exemptions for non-, in-, and out-migrants for a given level of geography; state and county. • The data contain geographically specific in- and out-migration flow-totals for a given level of geography; county-to-county and state-to-state. • For example, the number of returns and exemptions flowing from Baltimore County, Maryland to New York County, New York. • SOI formats and prepares the data for public release.

10. Analysis • Migration is closely related to age, population change, and economic conditions. • Migration statistics provide rich information about demographic and economic processes. • The following four slides will show how IRS migration statistics help researchers and analysts understand levels and trends in demographic, geographic, and economic processes.

15. Future Plans • In 2007, the Census Bureau’s Population Division moved from a ‘return-based’ system to a ‘person-based’ system of quantifying migration to enhance estimates accuracy. • Return-based: The total number of exemptions reported by the tax filer was used to determine the number of exemptions for that tax return at that level of geography. • Person-based: The total number of exemptions are based on the number of people listed.

16. Future Plans • Measuring migration at the person level, as opposed to the tax return level, allows one to estimate migration during major life-course events: • Filing your 1st tax return, marriage, divorce, etc. • Post 2010, the Census Bureau plans to provide ‘person-based’ migration total-flows by estimates geography to the IRS instead of the ‘return-based’ totals. • Data will provide a more accurate representation of actual migration totals and flows. • The number of tax returns will no longer be reported • The Census Bureau’s Population Division does not produce household level migration statistics.

17. Conclusion • Migration research is critical in studying population change because migration re-distributes existing population throughout space and time. • IRS migration data, representing approximately 80% of the U.S. population, is the largest administrative records based data source to estimate migration. • The move from a ‘return-based’ to a ‘person-based’ migration product is based on enhancing estimates accuracy. • Data is more in line with official Census Bureau population estimates methodology and data products. • Quantities of migration are based on the actual number of people moving; not based on number of people reported moving by the tax filer.

18. Contact information Caleb M Miller (301) 763-3529 caleb.m.miller@census.gov