By looking at where people were born instead of where they ultimately move to and die, geographic disparities in mortality look different than previously assumed, according to a new study published on April 1, 2023, in the journal Demography.

interstate migration may mitigate regional inequalities in mortality according to “Understanding Geographic Disparities in Mortality,” a paper led by Jason Fletcher, professor in the La Follette School of Public Affairs at the University of Wisconsin–Madison and director of the Center for Demography of Health and Aging with an appointment in Population Health Sciences.

“At a time when nearly a third of Americans die in a state they were not born in, it is important to consider how calculating geographic disparities in life expectancy does not only reflect the overall health of a region,” says Fletcher. “It also reflects migration patterns.”

Fletcher and his team of researchers were able to reconceptualize this important demographic measure by analyzing a sample of nearly 1.5 million individuals from the newly available Mortality Disparities in American Communities data set, which links respondents in the 2008 American Community Survey to official death records from the National Death Index. The currently available mortality follow-up period extends until Dec. 31, 2015.

By looking at state of birth instead of state of residence, all states except Minnesota in the Mid-Atlantic and Midwest regions of the U.S. have higher life expectancy measures. The opposite is true for almost all states in the southeastern region of the country, which already had the lowest life expectancies by state of residence.

For five states in the Southeast, male life expectancy of transplants to the state is more than two years higher than that of people born in the state who still lived there at the time of the 2008 survey used in the study.

The patterns for women are similar, but differences are slightly smaller in magnitude. This gender difference could be because the overall migration rate is higher for men than for women.

This new method of assessing regional life expectancy also demonstrates that interstate migration is not as simple as people selecting destinations based on health environments. Instead, states lose healthy residents to other states while they also gain healthy transplants.

The net effect differs widely across states but is clustered by region. For example, in many southern states, the mortality risk of transplants is much lower than the mortality risk of people who have remained in their home state. In many states in the Northeast and Midwest, the mortality risk of these two subgroups is similar.

However, migration patterns reduce these regional disparities, making them less visible in nearly all previous research on this topic that used state of residence in their measurements.

The Population Association of America featured this paper in the lead-up to their 2023 Annual Meeting in New Orleans from April 12-15, 2023.

Fletcher is a leader in the emerging field of social genomics, and this new paper is part of a larger research agenda that connects early life conditions and mortality. He was recently awarded the prestigious 2023 Guggenheim Fellowship to further this research.