Of course, statisticians already knew of one excellent way to establish causation in a more general sense: the randomized controlled trial (RCT). But such a study would be neither feasible nor ethical in the case of smoking. How could you assign people chosen at random to smoke for decades, possibly ruining their health, just to see if they would get lung cancer after thirty years? It’s impossible to imagine anyone outside North Korea “volunteering” for such a study.
