Detecting the effect of medical care on mortality

Objectives: To demonstrate an important limitation of empirical tests of the proposition that medical care has contributed to long-term declines in mortality. Quasi-experiments cannot detect the effect of care that sustain, rather than change, a downward trajectory. We demonstrate this limitation by testing two hypotheses. One is that isolation of patients and antibiotic treatment coincided with declines in tuberculosis (TB) mortality in Massachusetts between 1850 and 1950. Another is that the introduction of Medicare in the 1960s increased life expectancy at age 65. Results: The first hypothesis is supported, for both patient isolation and streptomycin. The second is not. The circumstances that could yield such results are explored. Conclusions: Epidemiologists and historians should cooperate to devise methods that can resolve the issue of whether medical care has sustained the steady downward trend in mortality witnessed over the last century-and-a-half.