Several of the U.S. Census Bureau’s surveys measure geographic mobility. This paper focuses on 2013 migration data collected through two different surveys, the American Community Survey (ACS) and the Annual Social and Economic Supplement (ASEC) of the Current Population Survey.

The ASEC offers a historical perspective on annual migration that is unparalleled. It first asked respondents about their movement in 1948. Data are available at the national and regional levels. There are two important, additional measures offered by ASEC: reason for move and distance moved. Neither is currently available through the ACS.

While the ACS cannot highlight long-term trends, its strengths include the ability to focus on smaller geographies and populations. Migration data are available to the city/town level. There are also ACS flow products available down to the county level. This level of detail is too refined for ASEC migration data.

Even though the two surveys have similar migration questions, design and methodological differences result in different estimates. This paper discusses these differences and notes changes since full ACS implementation in 2005. The analysis evaluates national mover rates for each survey, and includes an exercise to create a hypothetical ACS mover rate using only counties in the CPS sample to illustrate if county coverage in the CPS sample contributes to observable differences in mover rates between the surveys.

General guidance is provided regarding when to use the ACS or ASEC for migration estimates. The main conclusion of this paper is that there is no single, easily identifiable reason why migration estimates differ across these two surveys. Instead, there are a surplus of factors that each contribute to observed differences, which are summarized in a quick reference comparison matrix of the various factors provided in the appendix section. This is the first in a series of planned evaluations of Census migration data compared to other surveys, population estimates, and administrative records. Numerous elements discussed in this paper will be explored in-depth in future papers.