I know one thing, If Star Wars Episode 3 was released one week after Van Helsing, the percentage dropped will be allot higher. Maybe 80-89%. Its just a guess.
The film was ok, but this brings up an interesting question though. If the werewolves need the full moon to stay in such form, then how is it that the 1st werewolf was able to attack in broad daylight on what looked like to be an overcast day?