This appendix contains eight sections. Section 1 gives technical details of how we calculate standard errors in the CPS data. Section 2 discusses changes in the ACS procedures before 2005. Section 3 examines demographic and economic patterns in migration over the past two decades, in more detail than in the main paper. Section 4 examines the cross-sectional variance of location-occupation interactions in earnings when we define locations by MSAs instead of states. Section 5 describes alternative methods to estimate the variance of location-occupation interactions in income. Section 6 measures the segregation of industries across states and of occupations and industries across MSAs. Section 7 gives technical details on the use of SIPP and census data to calculate repeat and return migration rates. Section 8 discusses transition dynamics in the model.

We analyze the secular decline in interstate migration in the United States between 1991 and 2011. Gross flows of people across states are about 10 times larger than net flows, yet have declined by around 50 percent over the past 20 years. We argue that the fall in migration is due to a decline in the geographic specificity of returns to occupations, together with an increase in workers’ ability to learn about other locations before moving there, through information technology and inexpensive travel. These explanations find support in micro data on the distribution of earnings and occupations across space and on rates of repeat migration. Other explanations, including compositional changes, regional changes, and the rise in real incomes, do not fit the data. We develop a model to formalize the geographic-specificity and information mechanisms and show that a calibrated version is consistent with cross-sectional and time-series patterns of migration, occupations, and incomes. Our mechanisms can explain at least one-third and possibly all of the decline in gross migration since 1991.

We show that much of the recent reported decrease in interstate migration is a statistical artifact. Before 2006, the Census Bureau's imputation procedure for dealing with missing data inflated the estimated interstate migration rate. An undocumented change in the procedure corrected the problem starting in 2006, thus reducing the estimated migration rate. The change in imputation procedures explains 90 percent of the reported decrease in interstate migration between 2005 and 2006, and 42 percent of the decrease between 2000 (the recent high-water mark) and 2010. After we remove the effect of the change in procedures, we find that the annual interstate migration rate follows a smooth downward trend from 1996 to 2010. Contrary to popular belief, the 2007–2009 recession is not associated with any additional decrease in interstate migration relative to trend.

We show that much of the recent reported decrease in interstate migration is a statistical artifact. Before 2006, the Census Bureau’s imputation procedure for dealing with missing data in the Current Population Survey inflated the estimated interstate migration rate. An undocumented change in the procedure corrected the problem starting in 2006, thus reducing the estimated migration rate. The change in imputation procedures explains 90 percent of the reported decrease in interstate migration between 2005 and 2006, and 42 percent of the decrease between 2000 (the recent high-water mark) and 2010. After we remove the effect of the change in procedures, we find that the annual interstate migration rate follows a smooth downward trend from 1996 to 2010. Contrary to popular belief, the 2007–2009 recession is not associated with any additional decrease in interstate migration relative to trend.

Occupational licensure, one of the most significant labor market regulations in the United States, may restrict the interstate movement of workers. We analyze the interstate migration of 22 licensed occupations. Using an empirical strategy that controls for unobservable characteristics that drive long-distance moves, we find that the between-state migration rate for individuals in occupations with state-specific licensing exam requirements is 36 percent lower relative to members of other occupations. Members of licensed occupations with national licensing exams show no evidence of limited interstate migration. The size of this effect varies across occupations and appears to be tied to the state specificity of licensing requirements. We also provide evidence that the adoption of reciprocity agreements, which lower re-licensure costs, increases the interstate migration rate of lawyers. Based on our results, we estimate that the rise in occupational licensing can explain part of the documented decline in interstate migration and job transitions in the United States.