, Volume 42, Issue 1, pp 1-22

The role of public health improvements in health advances: The twentieth-century United States

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Mortality rates in the United States fell more rapidly during the late nineteenth and early twentieth centuries than in any other period in American history. This decline coincided with an epidemiological transition and the disappearance of a mortality “penalty” associated with living in urban areas. There is little empirical evidence and much unresolved debate about what caused these improvements, however. In this article, we report the causal influence of clean water technologies— filtration and chlorination—on mortality in major cities during the early twentieth century. Plausibly exogenous variation in the timing and location of technology adoption was used to identify these effects, and the validity of this identifying assumption is examined in detail. We found that clean water was responsible for nearly half the total mortality reduction in major cities, three quarters of the infant mortality reduction, and nearly two thirds of the child mortality reduction. Rough calculations suggest that the social rate of return to these technologies was greater than 23 to 1, with a cost per person-year saved by clean water of about $500 in 2003 dollars. Implications for developing countries are briefly considered.

Research support from the National Institute on Aging, Grant T32 AG00186, through the NBER is gratefully acknowledged. We thank Joe Harrington, as well as participants of the Harvard-MIT labor/development economics seminar and the Harvard Center for Population and Development Studies seminar, for their helpful comments; Kurt Keeley at the American Water Works Association for help in navigating historical data sources; municipal water and sanitation department employees too numerous to name for clarification of historical information; and Mireya Almazan and John Indellicate for their capable research assistance. A longer version of this article, which contains additional results not presented here, is available as NBER Working Paper No. 10511. All of our data are available on request, and all errors are our own.