tepped the most famous statistician of the age, Ronald Fisher, to insist that the statement should be, “smoking is associated with lung cancer.” He speculated that smoking and lung cancer might have a common cause, perhaps genetic. Fisher argued that establishing causation requires running an experiment where people are randomly assigned to smoke or not smoke and then observed for decades to see if they developed lung cancer. Such an experiment is unfeasible and unethical, to say nothing of the need to 