OTOH, people have been looking for evidence of nudging, and didn't find it. Since the a priori probability of a more than marginal effect of nudging is unlikely

OTOH, people have been looking for evidence of nudging, and didn't find it. Since the a priori probability of a more than marginal effect of nudging is unlikely, we can conclude that it's much more likely that nudging doesn't "work" than that it does.