New study led by Fletcher advances understanding of geographic health disparities

Photo of a globe.

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.

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, interstate migration may mitigate regional inequalities in mortality.

“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 (MDAC) data set, which links respondents in the 2008 American Community Survey (ACS) to official death records from the National Death Index. The currently available mortality follow-up period extends until December 31, 2015.

Portrait of Jason Fletcher, professor of public affairs
“It is important to consider how calculating geographic disparities in life expectancy does not only reflect the overall health of a region, it also reflects migration patterns,” said Jason Fletcher, the study’s lead author

By looking at state of birth instead of state of residence, all states in the Mid-Atlantic and Midwest regions of the U.S. except Minnesota 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 Southeastern region, 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.

This groundbreaking paper was featured by the Population Association of America 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.

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