County Reclassifications and Rural-Urban Mortality Disparities in the United States (1970-2018).

To demonstrate how inferences about rural-urban disparities in age-adjusted mortality are affected by the reclassification of rural and urban counties in the United States from 1970 to 2018. We compared estimates of rural-urban mortality disparities over time, produced through a time-varying classification of rural and urban counties, with counterfactual estimates of rural-urban disparities, assuming no changes in rural-urban classification since 1970. We evaluated mortality rates by decade of reclassification to assess selectivity in reclassification. We found that reclassification amplified rural-urban mortality disparities and accounted for more than 25% of the rural disadvantage observed from 1970 to 2018. Mortality rates were lower in counties that reclassified from rural to urban than in counties that remained rural. Estimates of changing rural-urban mortality differentials are significantly influenced by rural-urban reclassification. On average, counties that have remained classified as rural over time have elevated mortality. Longitudinal research on rural-urban health disparities must consider the methodological and substantive implications of reclassification. Attention to rural-urban reclassification is necessary when evaluating or justifying policy interventions focusing on geographic health disparities.