That is the topic of a recent paper by Catillon, Cutler and Getzen (2018). In 1800, life expectancy in the US was only 43 years; by 2014, this number had increased to 79 years. Using vital statistics data from the U.S. generally and specifically from the state of Massachusetts, they find the following:
…there is a stronger case that personal medicine affected health in the second half of the 20th century than in the preceding 150 years. Big medicine brought big benefits, especially to the older population, at big cost. In contrast, much of the health advance prior to the mid-20th century was a result of public health improvements, perhaps sometimes supported by physicians but not resulting from clinical therapies for individual patients.
Why is this? In 19th and first half of the 20th century, the big improvements in life expectancy were public health improvements. Providing clean water and sanitation resulted dramatic gains in survival, reducing water borne disease like typhoid fever and airborne diseases like tuberculosis. Specifically, Cutler and Miller (2005) found that 35% of the mortality reduction between 1900-1936 was due to improvements in clean water.
In 1940, the development of penicillin greatly reduced mortality from bacterial infections. In the second half of the 20th century, gains in health were largely due to medical treatments for cardiovascular diseases, largely heart attacks and stroke. Cutler, Rosen, and Vijan (2006) found that about half of the improvement in survival between 1960 and 2000 was a result of medical advances; a bulk of the remainder was due to lifestyle changes such as the reduction in smoking. In cancer, mortality reductions between 1900 and 2010 were due to improved screening (35%), behavioral changes such as reduced smoking (23%) and pharmaceutical innovation (20%).
They also ask whether the return on investment from medical spending has increased or decreased over time. They find:
Life expectancy is increasing, but not as fast as health care expenditures. Since 1935 spending per year of life gained increases. In the past two decades the cost effectiveness ratio has stabilized, but at a very high level.
Excess cost growth (i.e., the percentage point increase in health spending relative to the percentage point increase in GDP) averaged about 1% between 1900 and 1950, but between 1955 and 1970, excess cost growth was 3%, and averaged 2.7% between 1970 and 1995, decelerating to 1.5% over the past 20 years.
The authors also look ahead to what the future may portend. They cite 3 potential revolutions expected to arrive in the coming decades:
…a genetic revolution showing why common diseases occur and how they might be treated; an information revolution allowing clinicians to follow patients and their illnesses and individualize treatments; and a financial revolution in how medical care is paid for.