For a lot of the medical advances we had earlier in the 20th century, you didn't really need to do large-scale clinical studies to see if it was working. You gave someone an antibiotic, and they suddenly got much better. You gave people a polio vaccine, and they didn't get polio. You took someone's appendix out, and they didn't die.

It was really later in the 20th century, when medicine got more and more focused on treating and preventing long-term degenerative illnesses like cancer or heart attacks or high blood pressure, that it became more vital to measure the difference in a large-scale statistical way between how effective different types of treatment were over a long period of time.