The international diffusion of medical innovation since 1900: Revisiting the Preston curve

The health of nations has improved at an unprecedented rate since the start of the 20th century, following a series of waves of mortality declines. While the timing and intensity of these waves have been documented, the factors influencing their emergence and diffusion are still debated. This article examines the creation and adoption of health-enhancing technologies since the early stages of the epidemiological transition around 1900. We estimate health frontiers, as originally done by Preston (1975), to infer how health-enhancing knowledge develops and diffuses across countries. Our results show that the creation of health-enhancing innovation has been strongly income biased since 1900. Up to 1920, upward shifts in the health frontiers happened almost exclusively at high levels of income. After that and until 2000, we find evidence that health frontiers moved up at low levels of income with a delay of about 20-40 years, relative to upward shifts at high income levels. We also show that education does not confound our findings because factors other than income are also associated with life expectancy increases. Finally, we perform a growth accounting exercise suggesting that Western Europe and its Offshoots have mostly reached high health levels by pushing up the knowledge frontier, while the experience of the rest of the world is much more varied.