# Migration/Geographic Mobility

## Calculating Migration Expectancy Using ACS Data

The U.S. Census Bureau does not directly collect data on lifetime moves, but estimates on the average number of moves people make in a lifetime can be derived using age specific mobility rates in much the same manner that life expectancy and total fertility rates are calculated. The calculations are based upon a hypothetical cohort of 100,000 persons with mortality and 1-year mobility rates applied at each age group. The actual migration experience of individuals will vary from this average number and some individuals may have moved more than once in the 1-year period. A more accurate statement would be that these are actually the number of years in which the individual can expect to make one or more moves rather than actual number of moves.

The example below of migration expectancy is calculated using the population and number of nonmovers in the previous year by age estimated from the 2007 American Community Survey (ACS). These numbers are used to calculate an average mobility rate for each age group for the period selected (step 1). The number of movers appears in column L and the mobility rate (Rx) is automatically calculated in column B (step 2). A standard life table provides the expected population at the beginning of the age interval per 100,000 births (lx). The stationary population (Lx) is the total number of people still living in the age interval per 100,000 births as of the date of the NCHS - Life Tables, in this case, 2004 (step 3). The average mobility rate (Rx) is multiplied by the stationary population (Lx) to obtain the expected number of moves for each age interval (column E). These expected movers are cumulated across each age group from oldest to youngest (TMx), and then divided by the population still living per 100,000 born (lx), to obtain the average expected number of moves remaining for people in that age group (step 5).

Using 2007 ACS data, it is estimated that a person in the United States can expect to move 11.7 times in their lifetime based upon the current age structure and average rates and allowing for no more than one move per single year. At age 18, a person can expect to move another 9.1 times in their remaining lifetime, but by age 45, the expected number of moves is only 2.7.

1. Enter the total population 1 year and over and the number of nonmovers from table B07001 in columns I and J. The table can be accessed through the American FactFinder. For 1-year age intervals, the ACS public use microdata sample must be used. The files can be accessed through American FactFinder or DataFerrett  .
2. The number of movers will automatically tally in column L. The average rate will automatically be calculated in column B.
3. Enter the age specific “Number surviving I(x)” in column C and the “Person-years lived L(x)” in column D from the NCHS - Life Tables.
4. Expected movers (this age and cumulative) will be automatically calculated in columns E and F.
5. Number of expected moves left at that age will be automatically calculated in column G. This number will be calculated to 2 decimal places.
Excel Worksheets

References:
Long, Larry H. Migration and Residential Mobility in the United States. New York: Russell Sage Foundation, 1988, pp. 295-310.

Long, Larry H., and Celia G. Boertlein. The Geographical Mobility of Americans: An International Comparison. Washington, DC: U.S. Government Printing Office, 1976. Current Population Reports P23-64, pp 12-19.

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Source: U.S. Census Bureau | Migration/Geographic Mobility |  Last Revised: 2015-04-01T09:39:14-04:00