I'm saying that it is demonstrably negligible. For instance before the Casino Royale bond movie made it to cinemas leaks appeared and preemptively the studios made a fuss about this hurting box office figures. Somehow it managed to be the biggest bond release ever.

In fact I would state that the only thing really hurt by leaks are mid level movies that are not good enough to provoke people to go to the cinema.

Further to that I would assert, as others have, that people who often pirate often visit the cinema and would under no circumstances part with money for these mopvies so it economically changes nothing.