Ordinarily, though, if the money is spent, it will be noticed in one way or another. Leading up to the 1995 referendum, we knew perfectly well that the travel by people who came to Montreal represented expenses. But we did not know what the total cost was.
In that case too, I talked about that. When I was in Montreal, I had the privilege of being surrounded by better experts in voter behaviour. There was never any conclusive evidence that the rally benefited the "no" camp. In fact, a lot of people thought the opposite, that it had a backlash effect, that it was seen in such a bad light by the public that if it influenced people, it was in fact in the opposite direction.
That being said, I am the first to agree that no scientific opinion on a subject like that is absolute and final. We can't conduct experiments in a laboratory.