Unfortunately box office numbers aren't the relevant numbers to be looking at. You wouldn't expect piracy to have a huge impact on the box office, since seeing it in the theater and seeing it on the computer/television screen are either a) dissimilar enough experiences that there's no connection, or b) similar enough experiences that indicate the viewer was unlikely to see it theaters anyways. The meaningful numbers would be the various forms of home video - DVD/BlueRay, video-on-demand, rentals, streaming, broadcast revenue, etc. Unfortunately that is probably an impossible analysis due to complexity and lack of data. Since theatrical releases usually essentially function as a loss-leader (marketing costs usually exceed revenue) for home video, where Hollywood make the vast majority of their actually money (and usually begin to see actual profit), looking just at box office doesn't tell you anything about whether piracy impacts profits.
It would be more useful to look at, for example, video games where there is only revenue from initial sales.