How Money Walks – Technical Notes

The data presented on the “How Money Walks” website and through the “How Money Walks” mobile applications is obtained from the IRS Division of Statistics as well as the National Archives (for years prior to 1992).

• The IRS data contains numerous clerical errors, which have been corrected. These included: incorrect state codes for several states in several years, negative AGI migration numbers in several counties in the 1993-1994 file and incorrect amounts of income for non-migrants in several years and several counties. The data files for the years 1993-1994 are particularly problematic.
• The data is presented in nominal dollars, i.e. not adjusted for inflation.
• For years 1992-1994, the IRS reports total money income while all later years use adjusted gross income. Accordingly for years 1992-1994 the wealth migration data use total money income while all later years use adjusted gross income. While total money income and adjusted gross income are not the same, thing they are highly correlated and a reasonable proxy for the migration of income.
• Net migration totals for all counties in a state should add up to the net migration for the entire state as reported by the IRS. However, in a few cases (select states and select years) the sum of county migration totals does not add up to the total state migration. In such cases, the sum of county migration totals is used for the total state migration instead of the net migration as reported by the IRS. This is the case in several years and several states in the period 2005 to 2010.
• The migration statistics include both domestic and international migration.
• Data for Miami County prior to 2001 has been assigned to Miami-Dade County.
• The data provided by How Money Walks comes from the IRS and includes only people filing taxes. Population migration data represents the number of tax-filers, not the number of individuals. Migration of individuals who did not file taxes is not included in the dataset.
• IRS data prior to 1985 (1982 to 1984) is not used due to the large amount of errors contained within.

For further technical notes please refer to the IRS document “U.S. Population Migration Data: Strengths and Limitations.”

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