From one of the cited papers: "Ezzati et al. used Internal Revenue Service tax records that record movements from county to county to explore how much migratio

From one of the cited papers: "Ezzati et al. used Internal Revenue Service tax records that record movements from county to county to explore how much migration might explain disparities. They found that in general individuals moved from high life expectancy to low life expectancy communities and not the reverse. While their finding suggests migration may not be a major factor in the national patterns, it could be an important factor in selected counties that have experienced substantial in- or out-migration. On the other hand, net immigration of young Hispanic adults with lower mortality could have tended to increase life expectancy at birth for some counties and the nation as a whole."