Sure, but if the gains in an experiment come from cannibalizing other districts, then it's not a good guide to what will happen when everyone's in the experimen

Sure, but if the gains in an experiment come from cannibalizing other districts, then it's not a good guide to what will happen when everyone's in the experiment. Do you attract more people to the profession? Or do people get discouraged by seeing variable outcomes they can't predict ahead of time?