O'Brien S et al. N Engl J Med 2003;348:994-1004
Loosely paraphrased from Dr. Andrew Ko's lecture:
"A lot of times you might wonder what makes a clinical study significant or useful. There are a lot of ways to determine this, but a mentor of mine during my oncology fellowship at Stanford gave me this rule of thumb: if a person sitting in the back of the room can measure out the space of his or her thumb between the two survival curves on a Kaplan Meier graph, then the study is something to write home about."
Simple. Cute. Useful.